Electrical breakdown of insulators by one-carrier impact ionization

Abstract

Theories for current runaway by one-carrier impact ionization are generalized for insulators, in which the injected and ionizing charge carrier type is subject to trapping. Relations are derived for the critical current runaway field Fr and time to breakdown tr, and written in simple forms, offering physical insight into breakdown processes. A trapped charge of injected carriers is frequently established in the insulator, before a current runaway process develops. The breakdown relations show that the effect of such a trapped charge can be a significant increase in Fr and tr, as observed in several inorganic and organic insulators. The trapped charge is not always established on fast ramp tests. In such cases an anomalous range is predicted and observed in the breakdown characteristics, in which the breakdown field diminishes with decreasing time to breakdown. Breakdown models developed here will be found in the companion paper to offer consistent interpretations for observations on aluminum oxide.