Polymer multilayer films (MLFs) are promising for the next-generation film capacitors to reach the requirements of high energy density, high breakdown strength, and high temperature tolerance. Nevertheless, under extreme conditions, such as high temperatures and high AC electric fields, a dominating dielectric loss is found to be homocharge injection from the metal electrodes into the surface of polymer dielectric films and the subsequent charge recombination (i.e., AC electronic conduction) at the metal/polymer interfaces. In this work, high temperature polycarbonate (HTPC)/poly(vinylidene fluoride) (PVDF) MLFs with either HTPC (MLF@HTPC) or PVDF (MLF@PVDF) skin layers were used to study the mechanisms of charge injection. Using AC/DC breakdown and DC lifetime experiments, it was found that charge injection is more significant for MLF@PVDF than MLF@HTPC. Quantitative studies on dielectric losses from both ferroelectric switching of PVDF and AC electronic conduction were carried out using the electric displacement-electric field loop measurements. Based on the results, a dipolar electric double layer model at the metal/PVDF interfaces was proposed to explain the more significant charge injection and ferroelectric switching in MLF@PVDF than in MLF@HTPC. From these experimental results, we conclude that MLF@HTPC has enhanced breakdown strength and lifetime due to less charge injection and AC electronic conduction at high AC electric fields and high temperatures.

Enhancing breakdown strength and lifetime of multilayer dielectric films by using high temperature polycarbonate skin layers

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