Effects of plasma pretreatment on silicon nitride barrier films on polycarbonate substrates

Silicon nitride (SiNx) films deposited on Ar, N2, and O2 plasma-treated polycarbonate (PC) substrates have been investigated for transparent barrier applications. The details on different gas effects on PC surface and SiNx/PC properties were investigated in terms of the contact angle, free energy, roughness, adhesion, transmittance, water vapor transmission rate (WVTR) and oxygen transmission rate (OTR). It was found that both Ar and N2 plasma could improve the adhesion between SiNx films and PC substrates. When the roughness of plasma-treated PC substrates was decreased from 1.71 nm to 0.89 nm, the OTR data of SiNx/PC samples after 6000 times bending test was decreased from 0.61 to 0.1 cm3/m2/day. Moreover, the transmittance and permeation results of SiNx/PC plasma-treated samples also show great dependence. After Ar plasma treatment for 60 s, the WVTR and OTR of the 50-nm-thick SiNx barrier coating on PC substrate after 6000 times bending test can decrease to a value of near 0.01 g/m2/day and 0.1 cm3/m2/day, respectively. This result indicates that the SiNx films on Ar plasma-treated PC substrates have high potential for flexible organic light-emitting diode applications.