Effect of a hard coat layer on buckle delamination of thin ITO layers on a compliant elasto-plastic substrate: An experimental-numerical approach

Layer buckling and delamination is a common interfacial failure phenomenon in thin film multi-layer structures that are used in flexible display applications. Typically, the substrate is coated on both sides with a hybrid coating, called a hard coat (HC), which acts as a gas barrier and also increases the scratch resistance. In this paper 250nm thick indium tin oxide (ITO) layers have been deposited on a 200μm thick high temperature aromatic polyester substrate (Arylite^TM), with and without a 3μm HC. In order to study the influence of this HC layer on delamination phenomena, two-point bending experiments are performed from which buckle width and height values are measured after straightening of the sample. An analytical model and a finite element (FE) model are developed to estimate the adhesion properties from the measured buckle geometries. In the numerical model, the initiation and propagation of the delamination process is described by cohesive zone elements, of which the parameters are extracted from response surface model (RSM) results. Furthermore, the numerical model is used to illustrate the significant change in buckle geometry upon load reversal, i.e. from loaded to straightened state, which is governed by the elasto-plastic behavior of the substrate material. It is concluded that the addition of a HC layer significantly decreases the adhesion of the ITO layer. The latter is determined as function of the actual mode angle.