Magnetically actuated peel test for thin film interfacial fracture and fatigue characterization

Abstract

Delamination along thin film interfaces is a prevalent failure mechanism in microelectronic, photonic, MEMS, and other engineering applications. Current interfacial fracture test techniques specific to thin films are limited by either sophisticated mechanical fixturing, physical contact near the crack tip, non-representative test specimens, or complicated stress fields. Moreover, these techniques are generally not suitable for investigating fatigue crack propagation under cyclical loading. A fixtureless and noncontact experimental test technique is thus proposed and implemented to study interfacial fracture for thin film systems. The proposed test incorporates permanent magnets surface mounted onto micro-fabricated released thin film structures. An applied external magnetic field induces noncontact monotonic or fatigue loading to initiate delamination along the interface between the thin film and underlying substrate. Characterization of the film deflection, peel angle, and delamination propagation is accomplished through in situ optical techniques. Analytical and finite-element models are used to extract fracture parameters from the experimental data using thin-film peel mechanics. The developed interfacial fracture test has been demonstrated for Cu thin films on a SiO₂/Si substrate.