Dielectric Breakdown Characteristics of Biaxially Oriented Polypropylene Films: Surface Structures on Thickness Dependence

ABSTRACT Film capacitors, essential for energy storage in power systems, benefit from reduced film thickness to increase capacitance and lower costs. While the inverse power law traditionally links higher electric strength with thinner films, its validity diminishes below a critical thickness. This study investigates the thickness‐dependent dielectric breakdown characteristics (3.4–15 μm) of biaxially oriented polypropylene (BOPP) films under varying electrical polarities, focusing on surface structures, surface charge dynamics and trap mechanisms. Experimental results identify a transition thickness of 9 μm, beyond which the inverse power law holds. Below this threshold, breakdown field strength declines with thinning, correlating with reduced surface charge dissipation ratios and slower decay rates. Enhanced breakdown strength is observed when surface charge retention is higher. Additionally, thinner films exhibit proportional increases in shallow trap density, weakening dielectric performance. Excessive deep trap density further reduces breakdown strength. These findings highlight the critical role of surface effects and trap density in governing the dielectric stability of ultrathin BOPP films, providing insights for optimising capacitor film design.