Effects of current density on mechanical properties of electroplated nickel with high speed sulfamate bath.

In this work, defect-free and high mechanical strength nickel films are deposited at a high growth rate using a high concentration sulfamate bath for applications in fabrication of MEMS components. Effects of the applied current density on the morphology, average grain size, Vickers hardness, micro-mechanical property, and thickness distribution are studied. The average grain size is refined to a minimum value when the current density is increased from 10 to 20 mA/cm2. The finest grain size obtained is 349.8 nm. The grain refinement effect is a result of the promoted nucleation rate as the applied current density increased. When the current density is beyond 20 mA/cm2, overpotential of the nickel reduction reaction is lowered because of the promoted hydrogen evolution and causes coarsening of the average grain size. The film electroplated at 20 mA/cm2 shows a high growth rate at 0.296 μm/min, the highest Vickers hardness at 371 HV, and the yield stress evaluated by micro-compression test is 1.3 GPa. Relationship between the average grain size and the applied current density follows the Hall-Petch relationship well. Unlabelled Image • Defect-free Ni films were electroplated at a high growth rate using sulfamate bath. • The finest grain size at 349.8 nm was obtained when 20 mA/cm2 was used. • Ni with the finest grain size had hardness of 371 HV and yield stress of 860 MPa. • Grain size and strengths of the films followed the Hall-Petch relationship well. • Films plated at 10 & 20 mA/cm2 had uniform thickness distribution on the substrate. [ABSTRACT FROM AUTHOR]