Water and oxygen permeation of silicon nitride films prepared by plasma-enhanced chemical vapor deposition

Silicon nitride (SiNx) films deposited on flexible polyethersulfone (PES) substrates by plasma-enhanced chemical vapor deposition (PECVD) have been investigated for water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) barrier applications. Details of the NH3/SiH4 flow ratio and chamber pressure effects on the SiNx/PES properties in terms of chemical bonding, transmittance, refractive index, deposition rate, adhesion, roughness, OTR and WVTR were investigated. When the NH3/SiH4 flow ratio increased from 1.43 to 10, evident variations in refractive index and transmittance of the SiNx/PES samples were observed. Moreover, as the chamber pressure increases from 26.7 to 133.4 Pa, the deposition rate, adhesion and roughness increase while no evident variations in WVTR and OTR were observed. Under optimum conditions, the WVTR and OTR of 100-nm-thick SiNx barrier coating on PES at 150 °C decreased to a value of near 0.01 g/m2/day and 0.01 cm3/m2/day, respectively. This indicates that the SiNx barrier on PES has high potential for flexible display applications.