Investigation of Microwave Surface-Wave Plasma Deposited SiO_x Coatings on Polymeric Substrates

In this paper, we reported nano-scale SiO_x coatings deposited on polyethylene terephthalate (PET) webs by microwave surface-wave assisted plasma enhanced chemical vapor deposition for the purpose of improving their barrier properties. Oxygen (O₂) and hexamethyldisiloxane (HMDSO) were employed as oxidant gas and Si monomer during SiO_x deposition, respectively. Analysis by Fourier transform infrared spectroscope (FTIR) for chemical structure and observation by atomic force microscopy (AFM) for surface morphology of SiO_x coatings demonstrated that both chemical compounds and surface feature of coatings have a remarkable influence on the coating barrier properties. It is noted that the processing parameters play a critical role in the barrier properties of coatings. After optimization of the SiO_x coatings deposition conditions, i.e. the discharge power of 1500 W, 2:1 of O₂ : HMDSO ratio and working pressure of 20 Pa, a better barrier property was achieved in this work.