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This paper presents the development of nickel phosphorus (Ni-P) micromolding for the manufacturing of a 3D electrostatic energy harvesting microsystem. Ni-P alloy exhibits weak ferromagnetic properties beyond 10-12 wt% phosphorus content. Deposits were prepared at different current densities (−10 to −150 mA/cm 2 ) and concentration of phosphorous acid in the electrolyte (0-20 g/l). It was found that the deposition rate decreases when phosphorus content increases in the deposit. The final process leaded the choice of a H 3 PO 3 concentration of 5 g/l to reach a 0.1 μm/min deposition rate for phosphorus content higher than 13 wt%. Mechanical, electrical and magnetic properties of the Ni-P films were investigated on 1 mm 2 and 1 cm 2 square deposit and confirmed the suitability of that material for the target MEMS. Comb patterns of micromolded Ni-P have been realized on a 2-inch wafer, leading to a 10 μm thick deposit containing 13.5 wt% in P, which is, at our knowledge, the first high phosphorus Ni-P micromolding involving electrodeposition growth for 3D MEMS applications. The latest generation of pacemaker, lead-free, is directly implanted in the cardiac cavities of the heart, thus improving considerably patient comfort and reducing complications with common pacemaker such as lead failure. However, leadless pacemakers should overcome several issues such as the limited lifespan of the lithium-based battery used to supply those pacemakers. This involves a surgery of the patient every 7 to 10 years, whereas about 45% of patients survive more than 10 years after their first pacemaker implantation.1 The challenge for improving pacemaker's lifetime explains the strong interest for harvesting energy from the heart, which is a long reliable energy source.Among the solution leading to a volume compatible with implantation in the heart by intravenous catheter, energy harvesting from inertial movement seems promising once its design challenges the very low fundamental heart beat frequencies (1-3 Hz).2 Our team has already proposed such a design for an out-of-plane overlap electrostatic energy harvesting MEMS that would be able to harvest about 10 μW in average power. 3 The final layout of the proposed device is presented in Figure 1. The device is 5.5 mm in diameter and will have a total height of 1 mm.The fabrication process of such device is compatible with other types of 3D MEMS and is based on an original additive process (Figure 2) combining alternative electroplating of a patterned structural material (nickel) and a sacrificial material (copper). Nickel and copper have been chosen respectively for their mechanical properties, their high growth rate and the high etching selectivity of copper against nickel during wet etching. Electroplating is a low cost, fast and simple fabrication process which makes it very suitable for thick film growth. When combined with a lithography step in the micromolding process, film patterning is achieved (Figure 2a) by localized growth inside the mold. Finally the process is completed by ...

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.

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