Buckle morphology of compressed inorganic thin layers on a polymer substrate

The structural integrity of thin-film multi-layer structures that are used, e.g. in displays are of paramount importance. Layer buckling and delamination is a common interfacial failure phenomenon in these structures. In this paper plasma enhanced chemical vapor deposition has been used to grow a silicon nitride layer (Si3N4), 400 nm thick, on a high temperature aromatic polyester substrate spin coated with a silica-acrylate hybrid coating. Two-loading mechanisms are discussed: biaxial-compressive residual stress and uniaxial-compressive external stress. The influence of loading mechanism and level of adhesion on buckle morphology has been investigated. Telephone-cord and straight buckling are observed when the layer was under biaxial-compressive residual stress while circular buckling is observed when the layer was under additional uniaxial-compressive external stress. Oxygen plasma treatment is found to enhance buckling of the Si3N4 layer from the polymer substrate. The buckle width and heights are found to increase with the uniaxial-compressive external strain.