information systems increasingly leave fixed locations and appear in
our pockets and palms, they are getting closer to the physical
world, creating new opportunities for perceiving and controlling our
machines, structures and environments. To exploit these
opportunities, information systems will need to sense and act as
well as compute. Investing engineered systems with superior
capabilities to sense and act is the focus for our research
activities in microelectromechanical systems (MEMS).
Mellon University’s MEMS Laboratory is housed in the Electrical
and Computer Engineering Department and is part of The Robotics
Institute and the Institute
for Complex Engineered Systems. The MEMS Laboratory is engaged
in research on sensor and actuator systems with performance derived
from mechanical features measured in microns and components
numbering from a few to millions. Our research activities are
focused on design of batch-fabricated electromechanical devices and
development of related processes that leverage the enormous
investment in mature VLSI process technologies. The beneficial
attributes of batch-fabricated MEMS are low manufacturing cost,
miniaturization, and integration.
primary research thrust is toward highly integrated microsystems
that interact with the environment and push the boundaries of
electrical-mechanical functional integration. To achieve this
vision, we are developing two core technologies: MEMS integrated
with conventional CMOS (Complementary Metal-Oxide-Semiconductor)
electronics; and computer-aided design (CAD) methodologies and tools
for MEMS. Current projects include inertial measurement systems,
magnetic probe-based data storage, biologically inspired MEMS,
ultrasonic imaging arrays, lumped-parameter modeling of
electrostatic gaps and damping, schematic capture and synthesis
tools for MEMS, and process development and device characterization
of microelectromechanical structures made using CMOS processes.
Fabrication and Applications
group has developed a unique process to create electrostatically
actuated microstructures with high-aspect-ratio composite-beam
suspensions using conventional CMOS processing, followed by a
sequence of maskless dry-etching steps. Devices being made with the
CMOS-MEMS process include x-z microstages for a probe-based
mass-data-storage system on a chip, biologically inspired
microsensors, ultrasonic sensor arrays, and accelerometers and
gyroscopes for an on-chip inertial measurement unit. Supportive
efforts include design and analysis of metrology test structures,
modeling of device physics, and development of process enhancements.
example device, the two-axis lateral x-y microresonator shown in the
figure, has a central plate mass suspended by spring flexures and
actuated by electrostatic comb-finger drives. High-performance CMOS
may be placed within 15 µm of a micromechanical device, thereby
providing ultra-sensitive capacitive motion sensing with parasitic
capacitance as low as 13 fF. The ability to place multiple
conductors within a single mechanical structure is an extra degree
of design freedom allowing novel electrostatic actuators to be
fabricated. We are exploiting these and other features of CMOS
micromachining to create low-cost, high-performance sensor and
on image below for larger version)
plot of number of transistors merged with number of mechanical
components for existing and future MEMS devices and systems.
and Design of MEMS
sensor and actuators systems require integration of micromechanical
sensors and actuators with control, communications, data processing,
test, and calibration functions. With increasing functionality comes
a subsequent increase in complexity and a need for advances in
coupled-energy-domain system-level design. In the NODAS project, we
are creating a circuit-level tool for nodal simulation of suspended
microelectromechanical systems with an underlying hierarchical
representation which is intuitive to the MEMS designer. At the
high-end of the design spectrum, we are developing
optimization-based synthesis tools for microresonators and inertial
sensors. Our design research encompasses a range of activities:
control of sensor arrays, understanding micromechanical system
dynamics (e.g., gyroscopes), and parametric modeling and
experimental verification of physical devices.
electron micrograph of a released two-axis electrostatic-comb-drive
resonator made using the CMU CMOS micromachining process.
testing is primarily accomplished on our Wentworth MP-901 wafer
probestation, fitted with eight precision manipulators and a
high-resolution camera. Researchers have access to a 4000
square-foot, Class 100 cleanroom within the ECE department housing
state-of-the-art fabrication equipment. We use several CAD tools
including MATLAB Simulink, Cadence and Saber simulators; and Ansoft
Maxwell, MEMCAD, SDRC I-DEAS and ABAQUS finite-element packages.
future and real promise of MEMS will be in our ability to design
systems of components with thousands to millions of
electromechanical parts integrated with electronics to create MEMS
arrays with a systems function greater than the sum of the
individual parts. The figure to the right illustrates MEMS
electromechanical integration. The vertical axis is increasing
number of transistors and the horizontal axis is increasing number
of mechanical components. To first order, the number of transistors
are a measure of information processing capability and similarly,
the number of mechanical components are a measure of the ability to
sense and act. Mapped on the chart are not only past MEMS devices
and selected commercial MEMS devices and systems, but also regions
of electrical-mechanical integration that will enable future MEMS
next stage in the evolution and maturity of MEMS will be driven less
by captive fabrication facilities and process development and more
by innovative, aggressive electromechanical systems design. MEMS is
poised to take full advantage of advances in information technology
and couple them to advances in robotics and control theory to drive
a fundamentally new approach to electromechanical system design and
fabrication. For the first time, approaches akin to VLSI electronics
can be taken to usher in an equally exciting and productive era of
VLSI electromechanics. By merging sensing and actuation with
computation, MEMS will not only invest existing systems with
enhanced capabilities and reliability, but will make possible
radically new devices and systems designs that exploit the
miniaturization, multiplicity and microelectronics of MEMS.
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Computation,” IEEE Computational Science and Engineering Journal,
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IMECE: The Winter Annual Meeting of ASME in the 8th Symposium on
MEMS, Dallas, TX, November 16-21, 1997.
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Actuators A, vol. 57, no. 2, pp. 103-110, 1996.
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Polysilicon Microstructure,” IEEE Journal on MEMS, vol. 5, no. 4,
pp. 283-297, 1996.
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Pneumatic Actuators,” Technical Proceedings of MEMS ‘92,
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