Adhesion and environmental durability of anti-reflective coatings on cycloolefin copolymer

Antireflective (AR) coatings on cycloolefin copolymer (COC) substrates are widely used in automotive and smartphone camera systems. However, they face problems with poor interfacial adhesion and stress cracking in environmental tests. This study aims to improve the adhesion of AR coatings on COC substrates by ion-assisted deposition (IAD) through investigating the surface pre-treatment by ion bombarding and the selection of the first-layer material. We further investigate the relationship between the residual stress states (high tensile, low tensile, and moderate compressive) of as-deposited AR coatings and their crack resistance during the environmental test. The results show that optimal surface pre-treatment parameters are low ion energy and moderate treatment time (100 V, 1.5 A, 10 s), under which the critical load of the SiO₂ film (without IAD) increases by 19.6% compared to untreated samples. The reasons for the improved adhesion after surface pre-treatment are the increased wettability of the COC substrate (lower water contact angle) and the enhanced interfacial diffusion (higher surface roughness). The SiO₂ layer shows better adhesion than TiO₂ on COC, with the best adhesion achieved using porous SiO₂ deposited without IAD as the first-layer material. Moreover, AR coatings with as-deposited compressive residual stress exhibit the longest time to crack initiation, as this compressive stress partially offsets tensile stress generated by high temperature and humidity during the environmental test.