Differentiation of roughness and surface defect impact on dielectric strength of polymeric thin films

Increasing the dielectric strength of polymer films has been a key theme as it is directly responsible for increasing energy density of relevant components such as film capacitors and insulation tapes. Dielectric films with higher roughness and surface defects are subject to the formation of an air gap at the interface between dielectric film and metallised polymer electrodes, which results in inaccurate dielectric strength. The air gap due to roughness was found to result in dielectric strength of 25% higher than that using depositing metal on dielectric films (integral electrode). The integral electrode method is proven to be a better way to test the genuine dielectric strength of thin and rough dielectric films. Surface defects, on the other hand, were revealed to cause lowering of dielectric strength because of their contribution to the localised electric field and charge injection. The detrimental effect of surface defects can be suppressed by submerging the film in oil or coating the film with an oxide layer.