ABSTRACT
Title: DESIGN, FABRICATION, AND
CHARACTERIZATION OF A ROTARY
VARIABLE-CAPACITANCE MICROMOTOR
SUPPORTED ON MICROBALL BEARINGS
Nima Ghalichechian, Doctor of Philosophy,
2007
Directed By: Professor Reza Ghodssi, Department of
Electrical and Computer Engineering
The design, fabrication, and characterization of a rotary micromotor supported on
microball bearings are reported in this dissertation. This is the first demonstration of a
rotary micromachine with a robust mechanical support provided by microball-bearing
technology. One key challenge in the realization of a reliable micromachine, which is
successfully addressed in this work, is the development of a bearing that would result
in high stability, low friction, and high resistance to wear. A six-phase, rotary,
bottom-drive, variable-capacitance micromotor is designed and simulated using the
finite element method. The geometry of the micromotor is optimized based on the
simulation results. The development of the rotary machine is based on studies of
fabrication and testing of linear micromotors. The stator and rotor are fabricated
separately on silicon substrates and assembled with the stainless steel microballs.
Three layers of low-k benzocyclobutene (BCB) polymer, two layers of gold, and a
silicon microball housing are fabricated on the stator. The BCB dielectric film,
compared to conventional silicon dioxide insulating films, reduces the parasitic
capacitance between electrodes and the stator substrate. The microball housing and
salient structures (poles) are etched in the rotor and are coated with a silicon carbide
film to reduce friction. A characterization methodology is developed to measure and
extract the angular displacement, velocity, acceleration, torque, mechanical power,
coefficient of friction, and frictional force through non-contact techniques. A top
angular velocity of 517 rpm corresponding to the linear tip velocity of 324 mm/s is
measured. This is 44 times higher than the velocity achieved for linear micromotors
supported on microball bearings. Measurement of the transient response of the rotor
indicated that the torque is 5.62±0.5 micro N-m which is comparable to finite element
simulation results predicting 6.75 micro N-m. Such a robust rotary micromotor can be
used in developing micropumps which are highly demanded microsystems for fuel
delivery, drug delivery, cooling, and vacuum applications. Micromotors can also be
employed in micro scale surgery, assembly, propulsion, and actuation.
DESIGN, FABRICATION, AND CHARACTERIZATION OF A ROTARY
VARIABLE-CAPACITANCE MICROMOTOR SUPPORTED ON MICROBALL
BEARINGS
By
Nima Ghalichechian
Dissertation submitted to the Faculty of the Graduate School of the
University of Maryland, College Park, in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
2007
Advisory Committee:
Professor Reza Ghodssi, Chair
Professor Christopher Cadou
Professor Isaak Mayergoyz
Professor Robert Newcomb
Professor Martin Peckerar
© Copyright by
Nima Ghalichechian
2007
ii
Dedication
This work is dedicated to my father Yousef, my mother Mansoureh, my sister Sameh,
and my beloved Gulsah for their support and encouragement throughout my doctoral
study years.
iii
Acknowledgements
I would like to thank my advisor Prof. Reza Ghodssi for his guidance and support
throughout the five years of my graduate studies at the University of Maryland
(UMD). Thanks to my dissertation committee members Prof. Christopher Cadou,
Prof. Isaak Mayergoyz, Prof. Robert Newcomb, and Prof. Martin Peckerar. Special
thanks to Mr. Alireza Modafe from the MEMS Sensors and Actuators Lab (MSAL)
for mentoring me during the first few years of my graduate studies; I have benefited
greatly from our discussions, his insight and assistance. Thanks to Mr. Alex Frey who
helped me in developing the test setup. Many thanks to all members of the MSAL for
their assistance and constructive feedback, especially Stephan Koev, Matt McCarthy,
Mustafa Beyaz, C. Mike Waits, Brian Morgan, and Jonathan McGee. I have
significantly benefited from discussions with Prof. Isaak Mayergoyz from UMD on
fundamental concepts of synchronous machines and Prof. Jeffrey Lang from MIT on
motor design and testing. I am grateful to Dr. James O’Connor, Mr. Thomas
Loughran, and Mr. Jonathan Hummel from the Maryland Nanocenter clean room
facilities (FabLab) for their help with the fabrication. During this study, I have
benefited from collaboration with Dr. Mariano Anderle at ITC-irst, Italy on polymer-
metal interface study and the Army Research Laboratory (ARL), Adelphi, MD on the
development of rotary micromotor. Many thanks to Prof. Inderjit Chopra from
Department of Aerospace Engineering, UMD for his support. This project was
generously supported by the ARL under Grant No. CA#W911NF-05-2-0026, Army
Research Office under Grant No. ARMY-W911NF0410176, and the National
Science Foundation under Grant No. ECS-0224361.
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