SELF-HEALING PROCESS AND DC BREAKDOWN IN THERMALLY GROWN STEARIC-ACID THIN-FILMS

In this paper recent work on dc breakdown field strengths of stearic acid thin films prepared by thermal evaporation in vacuum is described. Since these vacuum-deposited films contained a relatively high density of weak spots, voids and/or inhomogeneities, their breakdown strengths were at least an order of magnitude lower than those of the corresponding specimens prepared by the dipping technique. Therefore, the specimens were first allowed to undergo a 'self-healing' process which resulted in an increase in the sample resistance and an improved breakdown strength. The nature of the self-healing process is qualitatively discussed considering some chemical changes and/or melting of the film between the electrodes. Further, the authors discuss two types of breakdowns, single hole and self-propagating, observed in vacuum-evaporated films. The voltage-time and voltage-current characteristics and micrographs of breakdowns in these films are illustrated. The breakdown process is believed to be an electronic-modified thermal event.