Interfacial Critical Energy Release Rate Research Articles

Cross-sectional nanoindentation: a new technique for thin film interfacial adhesion characterization

Interfacial adhesion is becoming a critical material property for improving the reliability of multilayer thin film structures used in microelectronics. Cross-sectional nanoindentation (CSN) is a new mechanical test especially designed for measuring the fracture toughness of thin film interfaces. Interfacial fracture is achieved by nanoindentation in the structure cross-section. A model based on the elastic plate theory has been developed to calculate numerically the interfacial critical energy release rate ( G ci) for ceramic–ceramic systems from CSN test results. The model inputs are the thin film elastic properties, thin film thickness, interfacial crack area and maximum thin film deflection during the test. Closed form analytical solutions, obtained for two limiting cases, are consistent with the numerical approach. This technique has been successfully applied to silicon nitride–silicon oxide thin films, commonly used as electrical isolators in microelectronic devices.

On the effects of friction, roughness and toughness on interfacial sliding in brittle composites

This computational analysis investigates the interaction between friction, roughness and toughness at interfaces with regard to sliding lengths which proceed from the tip of an impinging matrix fracture. Sliding lengths at interfaces are important to the fracture behavior of brittle fibrous composites. The computer model uses a two dimensional surface integral formulation to model a crack perpendicular to a nominally planar interface. The tractions at the interface satisfy a Coulomb relationship and are found through an iterative process involving the stress induced by the matrix crack, the stress induced by the developing slip and an initial normal compressive stress (presumed to result from setting and/or thermal coefficient mismatch). The interfacial roughness is simulated using surface integral elements arranged in a periodic, triangular array. The toughness of the interface is represented via a specialization of the surface integral formulation to embed the near-tip, elastic asymptotic solution. The results indicate that there are significant interaction effects between friction and the other parameters, i.e. the friction dictates the sensitivity of the sliding lengths to changes in interfacial toughness and roughness. Also, to achieve `long' sliding lengths, which may be desirable in reducing the stress concentration in the medium across the interface, the magnitude of the interfacial critical energy release rate must be significantly less than the magnitude required to ensure crack deflection.