X-shaped-spring enhanced MEMS electret generator for energy harvesting

X-shaped high-aspect-ratio parylene spring has been proposed for MEMS electret energy harvester in order to suppress the rotational motion of the seismic mass. A MEMS harvester prototype with the X-shaped spring is successfully microfabricated with parylene trench filling technology. The rotational angle has been reduced to 1/5 with the present spring structure, and 1.5 μW output power is obtained at 28 Hz and 0.5 g. The X-shaped spring also offers nonlinear behavior of the spring, which realizes a wide bandwidth of 16-28 Hz. In addition, interdigitated suspended electrodes have been prototyped for the parasitic capacitance reduction and thus for higher output power.