Titanium oxynitride (TiNxOy) films were deposited on polyethylene terephthalate (PET) substrates by means of a reactive radio frequency (RF) magnetron sputtering system in which the power density and substrate bias were the varied parameters. Experimental results show that the deposited TiNxOy films exhibited an amorphous or a columnar structure with fine crystalline dependent on power density. The deposition rate increases significantly in conjunction as the power density increases from 2 W/cm(2) to 7 W/cm(2). The maximum deposition rate occurs, as the substrate bias is -40 Vat a certain power densities chosen in this study. The film's roughness slightly decreases with increasing substrate bias. The TiNxOy films deposited at power densities above 4 W/cm(2) show a steady Ti:N:O ratio of about 1:1:0.8. The water vapor and oxygen transmission rates of the TiNxOy films reach values as low as 0.98 g/m(2)-day-atm and 0.60 cm(3)/m(2)-day-atm which are about 6 and 47 times lower than those of the uncoated PET substrate, respectively. These transmission rates are comparable to those of DLC, carbon-based and Al(2)O3 barrier films. Therefore, TiNxOy films are potential candidates to be used as a gas permeation barrier for PET substrate. (C) 2007 Elsevier B.V. All rights reserved.