A novel microfabrication of a self-aligned vertical comb drive on a single SOI wafer for optical MEMS applications

Abstract

A novel method for fabricating a self-aligned electrostatic vertical comb drive using a single layer of a SOI wafer is introduced. The fixed combs are anchored to bimorph cantilevers made of two materials with dissimilar thermal coefficients of expansion, i.e., silicon dioxide and single crystal silicon. The cantilever, which provides the vertical offset between the fixed comb and the movable comb, is deflected by residual stress during cooling down from oxidation temperature to room temperature. In piston motion, the vertical amplitude at the resonant frequency of 3.5 kHz is 30 µm. In torsional motion, the angle of optical deflection at the resonance of 830 Hz is changed by 6.5°. The measured resonant frequencies correspond to the results from a finite element analysis within 10%. This vertical comb drive is useful for optical and biophotonic MEMS requiring out-of-plane torsional or piston motion.