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 E1/2.