Probing Electronic Band Structures of Dielectric Polymers via Pre-Breakdown Conduction.

The electronic band structure, especially the defect states at the conduction band tail, dominates electron transport and electrical degradation of a dielectric material under an extremely high electric field, and the ability to probe such states provides insights into the mechanism of dielectric breakdown for better designs of new materials. However, the electronic band structure governing the charge transport in a dielectric is barely well studied due to experimental challenges in detecting the electrical conduction to an extremely high electric field, i.e., prebreakdown. In this work, we probe the electronic band structure of polymer dielectric films through a novel in-situ prebreakdown conduction measurement method in conjunction with a space-charge-limited-current spectroscopic analysis. An exponential distribution of defect states at the conduction band tail with varying trap levels is observed in accordance with the specific morphological disorder in the polymer dielectric, and the experimental defect states show also a favorable agreement with the calculated density of states from the density functional theory. The methodology demonstrated in this work bridges the molecule-structure-determined electronic band structure and the macro electrical conduction behavior, provides highly improved understanding of material properties that control the electrical breakdown, and paves a way for guiding the modification of existing material and the exploration of novel material for high electric field applications. This article is protected by copyright. All rights reserved.