Young's modulus of electroplated Ni thin film for MEMS applications

Abstract

The Young's modulus of an electroplated nickel (Ni) thin film suitable for microelectromechanical applications has been investigated as a function of process variables: the plating temperature and current density. It was found that the Young's modulus is approximately 205 GPa at plating temperatures less than 60 °C, close to that of bulk Ni, but drastically drops to approximately 100 GPa at 80 °C. The inclusion of ammonium and sulphate ions by hydrolysis is believed to be responsible for the sharp drop. The Young's modulus of 205 GPa is for a Ni film plated at J=2 mA/cm2 and it decreases to 85 GPa as the plating current density is increased to 30 mA/cm2. The results imply that at low current density, the plating speed is slow and there is sufficient time for the as-plated Ni atoms to rearrange to form a dense coating. At high currents, the plating speed is high, and the limited mass transport of Ni ions leads to a less dense coating.