Silicon oxynitride gas barrier coatings on poly(ether sulfone) by plasma-enhanced chemical vapor deposition

Thin silicon oxynitride (SiO_xN_y) has been deposited for a gas barrier layer on the surface of poly(ether sulfone) film using plasma-enhanced chemical vapor deposition (PECVD) of a mixture of hexamethyldisiloxane (HMDSO) and ammonia. The chemical structure of the deposited layer varied from organic to inorganic structures depending on RF plasma input power applied to the reaction system. A silicon-based undercoat layer, which has an organic/inorganic hybrid structure, was used as an interfacial buffer layer between the organic PES and inorganic SiO_xN_y layer. With the help of the undercoat layer, the dense inorganic SiO_xN_y layer gave a superior oxygen barrier property of 0.2 cm³/m² day at a critical coating thickness of ca. 20 nm. In a highly stressed SiO_xN_y film, the effect of the undercoat layer was remarkable in preventing crack formation during bending tests.