The effect of film thickness variations in periodic cracking: Analysis and experiments

Periodic cracking experiments are frequently used in the assessment of interface quality in brittle film/compliant substrate systems. Through these techniques it is possible to extract a quantitative measure of interface shear strength and therefore assess the mechanical suitability of the films for application. The influence of film thickness inhomogeneities on the crack spacing is assessed in this study. While film thickness inhomogeneities are always present in thin film systems, only nominal thickness values have been considered up to this point. By defining two separate regimes of film thickness variation, roughness and unevenness, in relation to the crack spacing, the influence of such variation on the data is analysed. The results of this analysis are then considered in reference to a model system of an amorphous alumina film on a copper substrate (AlxOy/Cu), the limits of this analysis are then discussed.