Plasma-deposited silicon oxide barrier films on polyethersulfone substrates: temperature and thickness effects

Silicon oxide (SiOx) films deposited on flexible polyethersulfone (PES) substrates by plasma-enhanced chemical vapor deposition (PEVCD) have been investigated for transparent barrier applications. Although the water vapor transmission rate (WVTR) of PES (similar to 28 g/m(2)/ day; thickness: 200 mu m) is higher than that of the polyethylene terephthalate (PET; similar to 16 g/m(2)/day; thickness: 188 mu m), the PES substrate can withstand process temperatures of up to 180 degrees C, providing more flexibility in the design of device processing. Details of the substrate-temperature and film-thickness effects on the SiOx/PES properties in terms of transmittance, refractive index, deposition rate, adhesion, roughness, and WVTR were described. When the substrate temperature increased from 80 to 170 degrees C, the deposition rate, adhesion, and roughness values were found to increase while the WVTR decreased to a value of near 0.3 g/m(2)/day at 150 degrees C. With increasing the oxide thickness from 50 to 500 nm, the surface roughness increased from 2.71 to 5.84 nm. A lower WVTR value can be achieved under a barrier thickness of 200 nm. Further improvement was carried out by depositing a 100-nm-thick SiOx film on both sides of the PES substrate, which resulted in a minimum WVTR of 0.1 g/m(2)/day. The double-sided coatings on PES could balance the stress and greatly improve the WVTR data. (c) 2004 Elsevier B.V All rights reserved.