Micro harvester using isotropic charging of electrets deposited on vertical sidewalls for conversion of 3D vibrational energy

Abstract

The design and fabrication process of an integrated micro energy harvester capable of harvesting electrical energy from low amplitude mechanical vibrations is presented. A specific feature of the presented energy harvester design is its capability to harvest vibrational energy from different directions (3D). This is done through an innovative approach of electrets placed on vertical sidewalls, allowing miniaturization of 3D capacitive energy harvester fabrication on monolithic CMOS substrates. A new simple electret charging method using ionic hair-dryers is used. The charging performance of SiO 2 and CYTOP electrets are characterized for electrets in horizontal arrangement and electrets deposited on vertical sidewalls.

MEMS Technologies for Energy Harvesting

“…Among the materials most commonly used for electrets we find inorganic layers made of SiO 2 , a combination of SiO 2 and Si 3 N 4 layers, [52], and also organic compounds based on polymers. Among the polymers compatible with MEMS processes we may find the amorphous perfluorinated polymer CYTOP (Asahi Glass Col., Ltd), [53,54,55,56]. This polymer can provide up to four times more charge density than Teflon.…”

“…Charges have also been successfully injected into electrets with very inexpensive equipment such as ionic hair-dryers, [56]. Corona charging generates principally surface charge whereas electron beam and thermal poling produce volume, surface charges and polarization.…”

“…The more conventional approach for using electrets includes planar electrets, [57], although they can also be deposited on vertical walls, [56,58]. Vertical electrets are more difficult to produce since for example the corona method or ion implantation cannot be used.…”

“…Fig. 21 a) Detail of the device proposed in [56], b) schematic of the overall device, c) cross section of the device (suspending beams not shown).…”

“…Examples of recent energy harvesters using electrets can be found in [57,56,59]. The authors in [57] propose an electrostatic energy harvester using an electret inside the active gap.…”