Electrical Properties of Thin Polymer Films. Part I. Thickness 500–2500 Å

Abstract

The current I through silicone polymer films formed by electron‐beam bombardment in the thickness range 500–2500 Å has been measured as a function of voltage and temperature between 4° and 300°K. The electrodes were vapor‐deposited films of various metals. The electron transport is nonlinear and depends on voltage and thickness only through the electric field E when the applied voltage is greater than 5 V. At and below five volts, a negative resistance phenomenon similar to that described by Hickmott is sometimes observed which is voltage dependent rather than field dependent. The high‐field electron transport depends rather strongly on temperature. The negative resistance phenomenon is not temperature dependent. The field‐dependent current changes with time as a result of the diffusion of oxygen into the film, and this change appears to be correlated with a change in electron spin resonance absorption. The effect of free radicals on the electron transport which is thereby suggested, is further confirmed by the increased current observed as a result of a relative increase in the electron beam intensity used in the film formation. A hysteresis observed in the electron transport may be due to high‐field polarization of the dielectric. The capacity of the specimens also changes with time, as a result of the diffusion of water into the dielectric. The usual theoretical expressions for field emission or Schottky emission do not completely fit the electron transport data although log I varies as E^1/2.