Micromechanical, vertical comb-drive-structures for the construction of an electrostatic energy harvester

Abstract:
The development of micromechanical energy harvesters establishes innovative supply options for self-powered nodes of multimodal sensor networks. In this work a novel electrostatic realization as vertical overlap type is demonstrated by design concept, topologies and microfabrication of single-layered test structures. This approach provides high areal densities of capacitance (Cmax in three-digit pF range for chip area =15x15 mm²), vertical deflections up to 100 µm and high capacitance ratios Cmax/Cmin for an enhanced output power. Technological main points are the deep reactive etching of comb electrodes with high aspect ratio (clearance =3 µm for depth =100 µm) and the manufacturing of a highly z-compliant spring guidance with acceptable transverse stiffness. In dynamic characterization first vibrometric measurements on released test structures prove their ability to oscillate, showing deflection amplitudes in the higher twodigit µm range. Considering design-related parasitics, quasistatic capacitance measurements show capacitance ratios up to Cmax/Cmin=3.8. The further realization of multilayered comb-drive structures with vertically isolated stator planes will lead to higher power densities for the intended mediate but continuous extraction of small amounts of electrical energy from ambient, low-frequent vibrations.