Effects of radio-frequency power on the microstructure, morphology and wetting property of the silicon oxide films on glass and polyethylene terephthalate substrates by magnetron sputtering

Silicon oxide films were deposited on glass and polyethylene terephthalate (PET) substrates by means of radio-frequency (RF) magnetron sputtering and the effects of the RF power on the microstructure, morphology, composition and wetting property of the films were investigated and compared. It was found that the films on PET have more voids and fissures than those on glass, especially those deposited with a RF power lower than 200 W, while the films on glass are all compact. All films possess the columnar structure and columns in the films on PET are coarser. These differences are supposed to result from the slower nucleation and faster diffusion on PET. Higher RF power provides particles with higher kinetic energy and produces films with denser structure and coarser columns. The silicon oxide films on both kinds of substrate have comparable thicknesses and compositions with an O/Si atomic ratio of 1.5. The surface roughness of the films is contributed from the roughness of substrate and the true roughness of films and the true roughness of films on both kinds of substrates reaches minimum at 200 W. The contact angle of water on the films shows a similar tendency, while the contact angle on PET is found lower than that on glass. The mechanism which explains the void formation of the film on PET can rationalize the difference.