Thickness dependence of a direct current breakdown field in stearic acid films

Abstract

Stearic acid films in the thickness range of 180–2000 Å were deposited by thermal evaporation in vacuum. The sandwich-type structures, Al–film–Al, were first self-healed by applying voltages lower than the breakdown voltages, and then their direct current (dc) breakdown fields (FB) were derived from the current–voltage characteristics. A power law dependence FB∝d−α, where d is the films thickness, and α≂0.5 and 1.0 have been found to fit the data in the respective thickness ranges of 600–2000 Å and 180–600 Å. The results have been discussed qualitatively in terms of the breakdown theories. The power law dependence FB∝d−α appears to be common to a wide variety of insulating thin films but α varies considerably depending on the insulator material, film thickness range, film deposition process and the testing method. The existing breakdown theories cannot explain the variation in α because they do not take into account the density of weak spots in the films.