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Using dynamic voltage drive in a parallel-plate electrostatic actuator for full-gap travel range and positioning

Publication Type:

Journal Article


(IEEE) Journal of Microelectromechanical Systems, Volume 15, Number 1, p.69-83 (2006)



Using dynamic voltage drive in a parallel-plate electrostatic actuator
for full-gap travel range and positioning

Rocha, L.A. Cretu, E. Wolffenbuttel, R.F.

Dept. of Microelectron., Delft Univ. of Technol., Netherlands;

This paper appears in: Microelectromechanical Systems, Journal of

Publication Date: Feb. 2006

Volume: 15, Issue: 1

On page(s): 69- 83

ISSN: 1057-7157

INSPEC Accession Number: 8771673

Digital Object Identifier: 10.1109/JMEMS.2005.859099

Posted online: 2006-02-06 08:52:28.0


The nonlinear dynamics of the parallel-plate electrostatically driven
microstructure have been investigated with the objective of finding
a dynamic voltage drive suitable for full-gap operation. Nonlinear
dynamic modeling with phase-portrait presentation of both position
and velocity of a realistic microstructure demonstrate that instability
is avoided by a timely and sufficient reduction of the drive voltage.
The simulation results are confirmed by experiments on devices fabricated
in an epi-poly process. A 5.5-V peak harmonic drive voltage with
frequency higher than 300 Hz allows repetitive microstructure motion
up to 70% of gap without position feedback. The results of the analysis
have been applied to the design of a new concept for positioning
beyond the static pull-in limitation that does include position feedback.
The measured instantaneous actuator displacement is compared with
the desired displacement setting and, unlike traditional feedback,
the voltage applied to the actuator is changed according to the comparison
result between two values. The "low" level is below the static pull-in
voltage and opposes the motion, thus bringing the structure back
into a stable regime, while the "high" level is larger than the static
pull-in voltage and will push the structure beyond the static pull-in
displacement. Operation is limited only by the position jitter due
to the time delay introduced by the readout circuits. Measurements
confirm flexible operation up to a mechanical stopper positioned
at 2 /spl mu/m of the 2.25 /spl mu/m wide gap with a 30 nm ripple.