Effect of substrate type on microhardness of multilayer thin film composite system

Abstract

Thin metallic multilayer films consisting of nanometer layer thickness deposited on different substrates have shown promising mechanical, electrical and magnetical properties, especially for applications in fabrication of microelectromechanical (MEMS) structures and wear-resistant applications. Electrodeposition of Ni/Cu multilayer films on substrates of (111)-oriented single crystal Si and 100μm-thick electrodeposited Ni film was carried out using dual-bath technique (DBT). The current density values was maintained at 10 mA cm-2 and projected thickness of deposit was 5μm. Vickers microhardness of Ni/Cu thin multilayer films was investigated. The substrate starts to contribute the measured hardness at penetration depths of the order of 0.07 - 0.20 times the film thickness. The measured “composite hardness” is a complex value that depends on the microstructure and the hardness of the film and the substrate and their relative differences. Ni/Cu films on (111)-oriented Si wafer and 100μm-thick electrodeposited Ni film as the substrates can be thought as “soft film on hard substrate” composite systems. Chicot-Lesage model based on the model for reinforced composites can be applied to experimental data for all specimen and the film hardness was calculated for each indentation diagonal. The values obtained for the film hardness HF are not constant for all types of these composite systems, but influenced by the applied load.