Influence of film structure on gas barrier properties of SiOxNy films

SiOxNy thin films were deposited on PET substrates by dc magnetron sputtering under various nitrogen gas flow ratios, and the influence of the nitrogen gas flow ratio on the gas barrier performance was examined on the basis of local structure of SiOxNy. The surface morphology of the films was evaluated by FE-SEM and AFM observations. The local structure of SiOxNy was determined by FT-IR analysis and measurement of refractive index. No obvious macro-defects, such as pinholes, were observed in the films and the surface morphology of all samples was similar. The film density increased with increasing nitrogen gas flow ratio during the deposition process. However, the gas barrier performance decreased with increasing nitrogen gas flow ratio. On the basis of FT-IR analysis, it was determined that the structure of the SiOxNy film was a random bonding model (RBM) structure and an increase in the nitrogen gas flow ratio caused an increase in hydrogen termination in the Si–O–N network. The degradation of gas barrier performance at a high nitrogen gas flow ratio is due to the discontinuous Si–O–N network caused by the hydrogen termination.