Monolithic Integration of Thick NDFeB Micro-Magnets into Mems: Application to Electromagnetic Energy Harvesting

This paper presents a fabrication process for patterning 50μm thick rare-earth micro-magnets on a free-standing silicon resonator integrated into an electromagnetic energy harvester. Patterning of the micro-magnet arrays on a millimeter-scale surface is achieved by sputtering a NdFeB film onto a silicon substrate with etched features, through a shadow-mask. The use of a pre-patterned silicon substrate reduces the build-up of stress within the NdFeB layer, thus preventing delamination, while defining the in-plane dimensions of the micro-magnets. As a proof-of-concept, a fabrication process is implemented to integrate the micro-magnet array into an energy harvester that exhibits a normalized power density of ≈0.8×10 ^-3 kg.s.m ^-3 for a device volume of ≈300mm ³ , which is comparable to state-of-the-art MEMS electromagnetic harvesters. This patterning approach is foreseen to facilitate the integration of high-performance magnets into MEMS.