Effects of Cr buffer layer thickness on the microstructure and the properties of Ni thin films deposited on polyimide substrate

Ni thin films were prepared on pre-treated polyimide (PI) substrates by ion beam assisted deposition (IBAD). Cr buffer layers with the thickness varied from 0 to 78.7 nm were deposited between the Ni films and the substrates. Effects of the Cr buffer layer thickness on the structural, mechanical and electrical properties of the Ni thin films were investigated. It was found that existence of Cr buffer layer obviously improved the quality of the Ni thin films. The optimum Cr buffer layer thickness was determined which gave the lowest surface roughness (Ra) and the highest temperature coefficient of resistivity (TCR) of Ni thin film. Mechanical measurements indicated that the nanohardness of the Ni films increased with the thickness of Cr buffer layer, while the residual stress of the films decreased and then increased. The decrease of resistivity and the increase of TCR were contributed to the improvement of crystallization degree of Ni films caused by the Cr buffer layer. Interdiffusion effect on the electrical properties was also analyzed by the description of interface resistance.