del Corro, P. G., M. Imboden, D. J. Bishop, and H. Pastoriza. "Comb Drive Designs With Minimized Levitation." Journal of Microelectromechanical Systems 25, no. 6 (2016): 1025–1032.
Abstract: This paper presents two capacitive comb drive
designs for electrostatic actuation of MEMS with the aim to
eliminate the levitation effect often observed in such systems.
By placing a shield over the comb drive fingers, it is possible
to balance the electric field and suppress vertical forces while
maintaining the desired lateral motion. By optimizing the comb
geometry, we demonstrate that our approach is able to reduce the
levitation by an order of magnitude and unwanted coupling of
motion from out-of-plane to in-plane by a factor of 7 compared
with standard comb architectures fabricated using PolyMUMPs
technology, without the need of alternating comb finger polarities
or additional control electrodes. Levitation was reduced to
160 nm, for 3.6-Âµm lateral displacement at a driving voltage
of 80 V.