On a Cumulative Model of Dielectric Breakdown in Solids

Dielectric breakdown in solids defies simple classification, and no existing theory is capable of accounting for the totality of the observed phenomena. However, the physical nature of the processes involved may be inferred from the statistical nature of breakdown, from the essential role of charge carriers and defects, and from the discreteness of the resulting breakdown channel. Analysis shows that classical avalanche phenomena are unlikely to be the dominant mechanism because charge carriers in the virgin materials do not normally have sufficient energy to cause the required damage. A cumulative model is proposed, based on the proposition that a smaller amount of energy is required to extend a pre-existing defect than to create one in the first place. Successive stages of the ¿conditioning¿ process of insulators by electric fields involve the creation of ¿clusters¿ of defects, their subsequent growth in the direction of the field, and the eventual joining of these elongated defects into a discrete breakdown channel. Breakdown at short times and in thin samples which occurs in many materials at fields of the order of 1 GV/m may be understood in terms of massive electron tunnelling through the image-force-lowered barrier, leading to rapid destruction of the material.