Ying,

A quick comment, since I don't know what material you were using:
Curling of comb fingers can be quantified not by film stress but
by film stress gradient.  You might have high stress gradient
despite low stress overall.

Since the curling direction is not consistent -- sometimes the
fingers curl upwards, is it possible that some film deposition
parameters are fluctuating?

Also, I am not sure about your overall mechanical design. But
when I worked with comb finger designs before, the length of
fingers are way shorter than 150 microns.  In fact I used a
typical length of 20 microns.  Your suspension is not likely to
have the stiffness to keep the moving fingers from the
stationary fingers when the vehicle moves too far away from its
relaxed position.

Patrick Cheung, research scientist   Xerox PARC, MS 35-1674
(O) 650-812-4338 (FAX) 650-812-4334   3333 Coyote Hill Road
[email protected]                  Palo Alto, CA 94304
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On Wed, 25 Feb 1998, Ying W. Hsu wrote:

Hello,
We have been making devices using comb drives.  One problem we have
encountered is the curling of fingers which resulted in fingers making
contact with electrodes underneath.  Sometimes the fingers curl up.  The
fingers are typically 150 microns long, 3 microns wide, and has 5
microns curvature.  The obvious suspects are film stress and poor
release.  Yet the film stress is about 10 Mpa, and standard release
procedures are being followed.  Has anyone solved this problem, and
achieved consistant yield?  Any comments, suggestions, or information
will be very much appreciated.

Ying Hsu
Irvine Sensors Corp.
3001 Redhill Ave.
Costa Mesa, CA