Temperature Coefficients of Resistance of Metallic Films in the Temperature Range 25° to 600°C

Abstract

The temperature coefficients of resistance (TCR) of films of sputteredAu, Ir, Mo,Ni, Pd, Pt, Rh, Ta, and W, of evaporated Al, Cr, Ti, and Zr, and of the alloy films Pt–Au, Pt–Ir, and Pt–Ni have been measured in vacuo over the temperature range 25° to 600°C; the film thickness range was 75 to 2000 A. The TCR values of films of the substantially pure metals were in the range ⅓ to ⅔ those of the respective bulk metals whether deposited on glass, Vycor, or Stupalith substrates. The departure of the conditions of growth of the film from those usual for the bulk metal, i.e., rapid cooling effects and impurities present, contributed imperfections which reduced the TCR of the film. The TCR values of alloy films were low, 0.0004 per °C for Au–Pt, and resistivities were 3 to 4 times that of either constituent. The TCR values of sputteredfilms of Mo, W, and Ta and of evaporated Cr, Zr, and Ti were generally less than 0.0001 per °C. Electron diffraction examination of films of these latter metals revealed oxide inclusions in the films. The presence of the oxide of the metal reduced the TCR and increased the R/sq of the film as compared to those of the pure metal. Only films of gold, platinum, and iridium were corrosion resistant in air near 600°C. Overcoats of evaporated SiO provided partial protection for the others. Powers up to 15 watts were dissipated by refractory metal films only 1 32 by ½ in. and about 750 A thick. These high values contrasted with less than ¼ w for a goldfilm of similar dimensions.