Micromolding of Ni-P for the Realization of a 3D Electrostatic Energy Harvesting MEMS

This paper presents the development of nickel phosphorous (Ni-P) micromolding for the manufacturing of a 3D electrostatic energy harvesting microsystem. Ni-P alloy exhibits weak ferromagnetic properties beyond 10-12 wt% P content. Deposits were prepared at different current densities (-10 to -150 mA/cm²) and concentration of phosphorous acid in the electrolyte (0 -20g/l). The rate decreases when phosphorous content increases in the deposit. The final process leaded to choose a H3PO3 concentration of 5 g/l which give a 0.1 µm/min deposition rate for P content higher than 13 wt%. Mechanical, electrical and magnetic properties of the Ni-P films were investigated on 1mm² and 1cm² deposits and confirmed the suitability of that material for the target MEMS. Comb patterns of Ni-P micromolding have been realized on 2 inch wafer, leading to a 10 µm thick deposit containing 13.5 wt% in P, which is, at our knowledge, the first Ni-P micromolding involving electrodeposition growth.