Performance improvement of a vibration-powered electromagnetic generator by reduced silicon surface roughness

This paper reports on a chemical polishing process suitable for p-type medium to high resistivity (17–33 Ωcm) silicon substrates. The chemical polishing process using an HNA solution of ratio 27:43:30 (hydrofluoric, fuming nitric, and acetic acids respectively). The process has been applied to the fabrication of a micromachined electromagnetic generator to reduce the sidewall surface roughness of the device after Deep Reactive Ion Etching (DRIE). The microgenerator converts external ambient vibration into electrical energy by electromagnetic transduction. Power output is limited by the maximum amplitude of movement which is in turn limited by the fracture strength of the etched silicon. By applying the polishing etch to the devices, the mechanical strength of the silicon structures increased from 2 N to 5.5 N (∼ 175% increase).