JMM 2006 Abstract
Design, Modeling, Fabrication and Testing of a High Aspect Ratio
Electrostatic Torsional MEMS Micromirror
As an essential part of an optical imager project, there was a need for a very
high aspect ratio MEMS optical scanning mirror (5 mm x 150 um clear aperture),
capable of a +-2 degree sweep at 1 kHz with an applied voltage less than 200 V.
This paper reports on the design, fabrication, modeling and testing of such
an electrostatically actuated MEMS mirror.
Fabrication involves using a <100> n-type double side polished silicon wafer,
along with surface and bulk micromachining techniques, to produce a mirror
with nickel torsion springs and nickel electrostatic actuators. There were
8 masks and 20 processing steps required. The performance of these devices
was measured and found to be within the required specifications.
Analysis involved developing models to predict the dynamic behavior of these
MEMS micromirrors. A basic parallel plate capacitor model was adjusted with
a finite element analysis to account for fringing fields. The Young’s modulus
of the electroplated nickel was determined to be 110 GPa from a comparison of
the model with the results of dynamic testing, and the residual strain test
structures led to a value of 0.0029 for the residual strain. Each of these
values are within the rather wide range of published values. Once these
values were determined, the model agreed very well with the measurements of
the dynamic angular response of the mirror.
K. Joudrey, G.G. Adams, and N.E. McGruer