Transparent Barrier Coatings on High Temperature Resisting Polymer Substrates for Flexible Electronic Applications

Silicon nitride (SiN x ) and parylene thin films were deposited onto flexible polyimide (PI) substrates using plasma-enhanced chemical vapor deposition and a parylene reactor for transparent barrier applications. The PI substrates from the Industry Technology Research Institute with high optical transmittance and high glass transition temperature were used. A relatively high growth temperature of 200°C was chosen to deposit the SiN x films. To characterize the SiN, films deposited under different growth temperatures, a wet-etching process was performed to visualize the defect distribution in the barrier films. After 120 min of etching, the etching area ratio decreased from 44.9 to 6.7%, while the average defect spacing increased from 125 to 450 μm with increasing growth temperature. Under room temperature and relative humidity of 50%, four SiN x /parylene stacks with the SiN x films deposited at 80 and 200°C were demonstrated to decrease the water vapor transmission rate to 7.9 × 10 -4 and 7.41 × 10 -6 g/m 2 /day, respectively. As a result, ultralow permeation can be achieved with less repeating barrier stacks by using high temperature deposited SiN x films in the barrier structures.