Fabrication of a vibration-driven electromagnetic energy harvester with integrated NdFeB/Ta multilayered micro-magnets

This paper describes the fabrication of MEMS-based electromagnetic energy harvesters for scavenging energy from the ambient vibration. The novel energy harvester is fabricated by bonding a vibrator with embedded micro-magnets and a stator with integrated microcoils. The micro-magnets are formed by using sputtering deposition of NdFeB/Ta multilayered magnetic films with a thickness of 10 νm and silicon molding techniques. High-aspect-ratio silicon micro-springs are fabricated using deep reactive ion etching to achieve large vibration amplitude. The microcoils fabricated by electroplating processes are serially connected for multiplication of the output voltages from individual magnet-coil units. The energy harvester is successfully fabricated and wire-bonded for characterization. The maximum voltage output of the energy harvester at 115 Hz is approximately 2 mV, which corresponds to a power density of 1.2 nW cm^-3. The performance of the energy harvester could be greatly improved by protecting the micro-magnets from oxidation and decreasing the spacing between the vibrator layer and the stator layer.