Silicon-Chip Based Electromagnetic Vibration Energy Harvesters Rapidly Fabricated by Wafer-Level Molten Metal Micro-Casting Technique

This paper reports a silicon-chip based electromagnetic vibration energy harvester that is fabricated with a wafer level micro casting technique to form on-chip integrated 3D metal solenoid and magnet sliding channel. The 150-turn solenoid is fabricated by rapidly casting molten ZnA1 alloy (at its low melting point of 380°C) into pre-micromachined silicon mold, where all the coils (wire cross sectional area=
$200\mu \mathrm{m}\times 40\mu \mathrm{m}$
) in the wafer are formed within 7 minutes. A sliding magnet responding to environmental vibration is put into the channel inside the solenoid to generate electricity. With the wafer-level energy harvester fabrication technique, the size of the harvester chip is as tiny as
$10.5\times 2.5\times 1.7\text{mm}$
. Test shows that the harvester collects environmental energy high-efficiently within frequency range of 17-47Hz and generates peak power of
$16.1\mu\mathrm{W}$
at 37Hz under 6.5g vibration. Compared to either non-MEMS wire-wound electromagnetic harvesters or normal on-chip piezoelectric/electrostatic ones, present on-chip EM harvester shows great improvement in volume power density.