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

Abstract

Polymer multilayer films (MLFs) hold a potential to achieve high energy density, high temperature rating, and high breakdown strength simultaneously for next-generation film capacitors. Under extreme conditions such as high AC electric fields and high temperatures, an important dielectric loss mechanism is the homocharge injection from metal electrodes and subsequent charge recombination (i.e., AC electronic conduction) at the electrode/dielectric interfaces. In this work, the mechanism of the AC electronic conduction loss is studied for high-temperature polycarbonate (HTPC)/poly(vinylidene fluoride) (PVDF) MLFs with either HTPC (MLF@HTPC) or PVDF skin layers (MLF@PVDF). Based on the DC/AC breakdown strength and lifetime measurements, it is observed that homocharge injection was more significant for MLF@PVDF than MLF@HTPC. Using the electric displacement-electric field loop analysis, dielectric losses from both AC electronic conduction and ferroelectric switching (PVDF) are quantified. A dipolar electric double layer model at the electrode/PVDF interfaces is proposed to explain the more significant ferroelectric switching and charge injection in MLF@PVDF. From these experimental results, it is concluded that enhanced breakdown strength and lifetime can be achieved for MLF@HTPC because of the reduced homocharge injection and AC electronic conduction at high electric fields and high temperatures.