Surface Modification Effects in Metallisation of Dielectric Films

Metallised film capacitors consist of polymer dielectrics and electrodes which are considered as two layers. Due to the huge difference in thickness of two layers, metallisation can affect the microstructure and properties of metallised films, resulting in the bilayer structure model may not accurately describing properties. In this work, metallised films are considered as a whole rather than two layers of dielectric and electrode, whereas the process of film metallisation is regarded as a surface modification of the dielectric film. Metallised films with different metal layer thicknesses are prepared by vacuum evaporation. We investigated the dielectric, electrical and self-healing properties of metallised films. Films with thicker electrode present higher dielectric constant, conductivity, energy density and lower breakdown strength. Thinner metal layers result in less self-healing energy and better self-healing property. The difference in properties is attributed to the surface modification of dielectric films by nanoscale metallisation. Thicker electrode contributes to smaller surface roughness, which increases the polarization and charge capacity of metallised films, but also implies worse self-healing property. Surface modification provides a new perspective for researching metallised films.