Environmental reliability and moisture barrier properties of silicon nitride and silicon oxide films using roll-to-roll plasma enhanced chemical vapor deposition

The moisture barrier properties and long-term reliability of flexible thin barrier films under harsh environmental conditions are crucial parameters to consider for the real-world applications of flexible electronics. In this study, we fabricated flexible barrier films of single-layer silicon nitride (SiN_x) and silicon oxide (SiO_x) on a polyethylene terephthalate substrate using plasma enhanced chemical vapor deposition. We investigated the stability and degradation mechanism of SiN_x and SiO_x barrier films at high temperature and under high humidity using water vapor transmission rate (WVTR) measurements and cyclic bending tests. The changes in chemical composition, film density, surface roughness, and WVTR were analyzed after environmental reliability tests. It was found that high temperature and high humidity induced oxidation of the SiN_x and SiO_x films, resulting in an increase in the surface roughness and decrease in the film density. The SiO_x film was oxidized faster than the SiN_x film and formed large hillocks on the surface. The WVTR values of both films increased as the reliability test time increased, especially under environmental conditions of 85 °C/85% relative humidity, with the barrier performance of the SiO_x film degrading more than the SiN_x film. The SiN_x film displayed stable barrier performance during 10,000 cycles bending test at a fixed bending radius of 10 mm, even after harsh environmental reliability tests.