Flatness Improvement of Double-Sided Magnetic Film for Narrow Gap Electromagnetic Energy Harvester

Abstract

This paper reports the design, modeling and preliminary fabrication result of the flatness improved magnetic film on a silicon structure for narrow-gap electromagnetic (EMG) vibration energy harvester (VEH). The harvester has double-sided corrugated shape silicon vibration mass with 15 µm-thick NdFeB permanent magnet. The narrower air-gap between the magnetic film and a counter coil electrode the higher output power. While the sputtered magnetic film shows good characteristics equivalent to a bulk magnet, it hinders to reduce the air-gap because the silicon structure was curved by its high residual stress. Applying the double-sided magnet to our previous device, the curvature radius of moving mass with 15 µm-thick NdFeB film was improved from 5.3 m to 40.1 m because of the stress compensation. With the narrowed 2 µm air-gap device, the resulting simulated output power is 48 µW that is 190 times as large as previous device.

Keywords

• MEMS
• energy harvester
• magnetic type
• NdFeB sputtering
• residual stress