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

摘要

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 deg C, close to that of bulk Ni, but drastically drops to approximately 100 GPa at 80 deg 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/cm~2 and it decreases to 85 GPa as the plating current density is increased to 30 mA/cm~2. 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.