Study on microstructure and its correlation with sheet resistance of Zn-Al metallized film

Zn-Al film was prepared on biaxially oriented polypropylene (BOPP) substrate via vacuum thermal evaporation. The microstructure and its correlation with sheet resistance of Zn-Al film were explored systematically. The results showed that the macromorphology of Zn-Al film was closely related to the surface topography of BOPP substrate. XRD and SEM analysis indicated that Zn-Al film displayed a columnar and strong textured structure of Zn (002). TEM results revealed that the film thickness was in the range of 20-25 nm, of which amorphous alumina was identified on/at the surface and interface, while Zn and a small amount of ZnO were detected in the middle. The amorphous alumina on the film surface prevented the further oxidation of Zn, and therefore helped to improve the stability of sheet resistance of the film. Nevertheless, the insulative alumina significantly decreased the film conductivity, which deteriorated the current handling ability of metallized film capacitors.