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Investigation of Multi-Layer
Actuation
Carlos R. Jimenez.
California State Polytechnic University,
Pomona.
Electrical Engineering, Fall 2006
Faculty Mentor: Professor Andrei Shkel.
Graduate Student Mentors: Max Perez,
Adam R. Schofield.
Department of Mechanical Aerospace
Engineering.
08-30-2005
Motivations for out of plane
actuation.

Currently fabricated X-Y axis
gyroscope driven by in-plane
actuation.

Desired X-Y-Z axis gyroscopes
driven by in-plane and out-ofplane actuation.
sense direction
Z
Driving
direction
Y
X
Y
X
Additional Sense
capabilities
© C. Jimenez 2005, IM-SURE
Out of Plane Actuation has a
wide range of applications
MEMS micro mirrors
For optical switching.
X-Y-Z Gyroscopes for
the aerospace and
automotive industry.
© C. Jimenez 2005, IM-SURE
How are lateral combs
actuated?

Regular lateral combs for inplane actuation driven by an AC
voltage signal.
+Vo-
Vo

Experimental concept for out-ofplane actuation driven by an AC
voltage signal.
+Vo-
Vo
t
t
© C. Jimenez 2005, IM-SURE
Motivations on using offset combs for
out-of-plain actuation vs. parallel plates.

SiO2
Limitations when fabricating structures in SiliconOn-Insulator for out-of-plane actuations.
V
Si
Electrode
Unfortunately current fabricating techniques do not allow
placing an electrode under a microstructure.
© C. Jimenez 2005, IM-SURE
Target objectives for the
research.




Model various lateral comb architectures in
Finite Element Analysis Software along
with MATLAB.
Design fabrication techniques to achieve
lateral combs with different heights.
Fabricate test structures to observe the
deepness differences in the combs.
Attempt to characterize structures.
© C. Jimenez 2005, IM-SURE
Modeling Results contd..
Force in the Z direction Vs Height of Ground Comb.
Constant
70 um
Changing
Height 0-70um
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Modeling Results contd..

Force in the Z Direction Vs. Potential
across Offset Combs
Variable Potential
From 0 to 100V
Ground
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Modeling Contd..
Out of Plane Force Vs. Comb Displacement.
-1.4e-12 N/um levitated
Force becomes
Negative after
A 25um rise.
Displacement.
© C. Jimenez 2005, IM-SURE
Fabrication parameters for force
Maximization

Sensitivity Analysis from the standard model.
Standard@35um
Tests: 15, 35, & 55um
Standard Gap@10um
Tests: 5,10 & 15 um
Standard Gap @10um. Tests: 5, 10 & 15um
© C. Jimenez 2005, IM-SURE
Designing test structures
Making and evaluating masks.


First approach: Opaque combs were thought to partially protect
combs from UV light when exposed.
Second approach: Create Structures with a two mask deposition.
This mask was not successful
for its
Unexpected roughness
Successful mask with
250um. resolution
© C. Jimenez 2005, IM-SURE
Smooth mask used to
fabricate the structure
Manufacturing devices
Lithography and etch for two mask process.







Apply a thick layer of Photo-Resist.
Protect the high combs with a first
mask and develop the wafer .
Hard Bake the wafer.
Apply a thin layer of Photo-resist.
Protect all combs with a second
mask and develop again
Deep etch for 90 minutes
Si
Deep etch for 45 more
minutes.
© C. Jimenez 2005, IM-SURE
Manufacturing Results
Evaluating the etching process

Despite the significant height
decrease, the final etch was not
evenly across the exposed combs.

A Dektek 3 surface profiler was
used to estimate the roughness
on the small comb surfaces.
Very rough
© C. Jimenez 2005, IM-SURE
Pre-Characterization
Isolating the Moving Structure

Between the combs we
deposited Sylgard182,
an elastomer with
flexible and isolating
properties.

Three days after,
the elastomer
cured, giving the
possibility for
electrical isolation.

The Characterization of the
test device was started but not
fully completed.
© C. Jimenez 2005, IM-SURE
How likely are offset combs to lift a
structure?
Standard in-plane vs. out-of plane forces.
© C. Jimenez 2005, IM-SURE
Full MEMS experience.
1.Idea
6.Characterization
5.Fabrication
2.Concept.
3.Modeling
4.Design
Layout
© C. Jimenez 2005, IM-SURE
Acknowledgments
Thanks to:

Faculty Mentor: Prof. Andrei Shkel

Graduate Student Mentors: Max Perez,
Adam Schofield.

Lab: Jesper Eklund, Max Perez, Adam
R. Schofield, Alexander Trusov,
Chandra S. Tupelly.

IM SURE: Said Shokair.

Calit2: Goran Matijasevic.
Funded by:
*National Science Foundation (NSF).
*Undergraduate Research Opportunity
Program (UROP).
© C. Jimenez 2005, IM-SURE
Questions?
© C. Jimenez 2005, IM-SURE
© C. Jimenez 2005, IM-SURE