Injection of a minimal space charge as mechanism for the initial phase of electrical polymer degradation

In this paper we present a model for polymer degradation during high-field stresses in analogy to the charge-to-breakdown concept in SiO ₂. The model is based on space charge injection under high fields which leads to a cumulative effect as in radiation damage. A critical total injected charge density Q_c is introduced, which is needed prior to any permanent damage. The assumption of a critical injection level explains the time and field dependence of the tree initiation time. The model is applied to electrical aging experiments in epoxy resins. It turns out that the critical charge for tree initiation is ~10 C/cm² similar to the value for trap creation in SiO₂ gate oxides