Evaluation of the interfacial strength of layered structures by indentation method

The delamination of thin coating films from substrates is a critical issue for the reliability of micro- and nanoelectronic devices. Indentation methods have the potential to measure interfacial strength in micro- and nanofilm thickness coating films. In this paper indentation tests of layered structures are simulated using the damage-based cohesive zone model. When the delamination initiates, the indentation load and depth curve tend to deviate from the indentation load and depth curve for the perfectly bonded case. When the interface is stiffer than the coating film, a brittlelike delamination occurs on the interface; when the stiffness of the interface is smaller than that of the coating layer a ductilelike delamination occurs on the interface. The ratio of shear moduli, mu(int)/mu(pI), characterizes the delamination behavior on the interface during indentation tests. Focusing on the discontinuous point during the indentation tests and introducing the balance of energy before and after the onset of delamination, the evaluation method of the interfacial strength is proposed. The proposed method can be used to estimate the interfacial strength when the ratio of hardness and the yield stress of the coating film is 3.5 < H-A/sigma(y)< 4.5.