Effect of Glass Transition Temperature on Enhanced Dielectric Breakdown Strength and Lifetime of Multilayer Polymer Films

High temperature, high energy density, and low loss dielectric films are promising candidates for miniaturized capacitors in electric vehicles and high-speed trains. However, single-component polymers could not achieve these desired properties simultaneously. Polymer multilayer films (MLFs), which combine a high dielectric constant polymer [e.g., poly(vinylidene fluoride) (PVDF)] and a high breakdown/low loss polymer [e.g., polycarbonate (PC)] in a unique layered structure, have the potential achieve them at the same time. In this work, the effects of PC glass transition temperature (T_g) on the dielectric insulation properties (breakdown strength and lifetime) were investigated at high temperatures of 100-150 °C. Three PC materials had T_g values of 145 (PC1), 165 (PC2), and 185 °C (PC3), respectively. It is observed that MLF-PC3 with the highest T_g of PC exhibited the highest Weibull direct/alternating current (DC/AC) breakdown strength and the longest DC/AC lifetime, whereas MLF-PC1 with the lowest T_g showed the lowest Weibull DC/AC breakdown strength and the shortest DC/AC lifetime. A high-temperature high-volage leakage current study revealed that MLF-PC3 exhibited the lowest bulk conductivity at all temperatures under different electric fields. The knowledge obtained from this study will help us design better MLFs with high performance for next-generation miniaturized capacitors.