Mechanical characterization of metallic thin films by bulge and scratch testing

The mechanical properties of 20-nm thick silver, titanium and nickel-chromium alloy films encapsulated between two silicon nitride ceramic layers are investigated by bulge and scratch tests. Bulge tests are used in order to measure the yield strength of the metallic films. An unexpected strain-softening behavior is observed for a silver sample, which is rationalized as a measurement artifact due to the delamination of the film from its substrate. An experimental workaround is proposed and shown to yield correct measurements. The adhesion strength of the metallic films is measured by scratch tests, and their failure mechanism is characterized by in-situ optical observations. All in all, the poorest mechanical properties are found in the silver. This is probably due to a combination of the low adhesion at the interface between the nitride and the metal and the low yield stress of the silver. •Combined mechanical testing of encapsulated metallic films as thin as 20nm•Bulge testing providing Young's modulus, residual stress and strength of the films•Scratch testing used for characterizing the adhesion properties of the films