Design analysis and fabrication of side-drive electrostatic micromotor by UV-SLIGA

Abstract

In the present work, a micro-electro-mechanical system (MEMS)-based electrostatic micromotor is designed and fabricated. Finite element analysis is done and various parameters affecting the torque are studied. Maximum torque is achieved at 120° phase angle. The effect of change in voltage, micromotor height and frequency is analysed and discussed. UV-SLIGA, a microfabrication technique, is used for the fabrication of electrostatic micromotor of height 30µm and higher. UV lithography is conducted by both positive AZ P4620 and negative (SU-8 10 and SU-8 2150) photoresists. Copper (Cu) is used as a sacrificial layer to release the rotor (the movable part) of the electrostatic micromotor. Electroformed nickel (Ni) is used for making stator, rotor and axle, whereas chromium (Cr) is used as a seed layer. The micromotor is fabricated with a stator-rotor pole having configuration ratio of 3:2. The gap between the rotor and axle is 20 µm. Wet chemical etching is used to etch the deposited metal layers (Cr, Ni and Cu). Challenges such as the adhesion between the photoresist mould and substrate, cracks, seepage and misalignment are faced during the microfabrication. These challenges are overcome by optimizing the various parameters. The fabrication of electrostatic micromotor is done successfully and the results are discussed in the article.