Some Effects of Gas upon the Resistance and Resistance-Temperature Coefficient of Sputtered Platinum Films

Abstract

Effects of oxygen and heat treatment on the resistance and temperature coefficient of resistance of sputtered Pt films.—Films 8 mm square were each sputtered in air at.02 mm on a blank kept at any desired temperature $T$ up to 450°C by means of a heating coil. Resistance temperature curves made in a vacuum of 1μ of Hg at temperatures below $T$ are reproducible straight lines. For "thin films" (resistance 500 ohms) the coefficient is negative but becomes positive by exposure to ${\mathrm{O}}_2$ while hot. Heat treatment alone will not cause a reversal in the coefficient. The effect of oxygen at room temperature on thin films sputtered cold is to decrease the resistance slightly, while if the films are sputtered hot and then cooled the effect is a slight increase. The resistance of very thin films when exposed to ${\mathrm{O}}_2$ at a temperature above a minimum (80 to 200°) depending on the film, increases very rapidly and would soon become infinite, but if cooled decreases again in time and soon reaches a value below the initial resistance. Other gases tried, ${\mathrm{H}}_2$, He and C${\mathrm{O}}_2$ had practically no effect. It is suggested that the low values of the temperature coefficient are due to ${\mathrm{H}}_2$ absorbed during sputtering and that the effects of the ${\mathrm{O}}_2$ are partly due to chemical action with the ${\mathrm{H}}_2$ and partly to absorption of the ${\mathrm{O}}_2$.