A Fundamental Stiction Model for Microassembly
A. A. Polycarpou*
University of Illinois

In many MEMS applications the dimensions of the components is relatively small, typically less than 100 mm. When such components come into contact, friction is relatively high with friction coefficients typically being larger than one, which is unacceptable. One such case is often encountered in microassembly where handling of small components is critical. In this research, a fundamental static friction (stiction) model will be developed from first principles and applied to typical microassembly components. The model will incorporate the roughness of the contacting surfaces, intermolecular forces, and possibly electrostatic forces.

Accelerated Testing of MEMS Structures and Devices
L. M. Phinney,* J. M. Jennings
University of Illinois

Before microelectromechanical systems (MEMS) devices can be mass produced and marketed, the reliability and operating lifetimes of these devices must be determined. This involves understanding how failures that affect MEMS devices behave at both operating and extreme, i.e., high temperature, conditions. Accelerated testing protocols can be developed once the relationship between the failure times at standard and extreme conditions are known. Also, the results of this investigation will provide further insight into MEMS failures and suggest future directions for research into the prevention of these failures. This project experimentally and analytically studies the failure of MEMS structures in order to establish accelerated testing procedures.

Capillary Forces at the Interface of a MEMS Probe and a Liquid
T. Saif,* L. Allen* (Mater. Sci. & Engr.), M. B. Wheeler* (Animal Sci.), C. Sager
National Science Foundation, ECS 98-07384

Capillary force allows small, flat, solid plates to float on liquids. The density of the plate material is higher than liquid. This project investigates the mechanisms of floatation and the force interaction between two small floating bodies. The project aims to identify the parameter space in which a MEMS probe can be used to manipulate an object in liquid without inundating the corresponding MEMS devices.

Development and Performance Measurement of MEMS Refrigeration System and Components
C. W. Bullard,* P. S. Hrnjak,* X. Tu
Defense Advanced Research Projects Agency

The focus of this project is on mechanical vapor compression systems in the range 1-5W. The choice of refrigerant, its effects on heat exchanger design, expansion device, and controls are studied. The focus this year is on design and building of an experimental facility capable of precise measurement of extremely low mass flow and heat transfer rates in the exchangers and other components.

Fabrication of Microminiature Devices and Microelectromechanical Systems
M. L. Philpott,* M. A. Shannon,* T. C. Tsao,* I. Adesida, T. A. DeTemple, K.-C. Hsieh, B. C. Wheeler (Elect. & Comput. Engr.)
Campus Critical Research Initiative Program

Applications for microelectromechanical systems (MEMS) which are being developed include low-cost micro-optical mechanical switches for telecommunications, mechanical devices for microsurgery, and masks for biological molecule deposition. This project is aimed at high force and displacement devices, as well as using dissimilar materials and creating 3-D utility from planar elements. One approach is to combine wafer-scale and laser-material processing to join elements that cannot be fabricated in the same process as silicon. Research in silicon and laser-material processing is currently being developed to solve fundamental issues of MEMS.

Integrated Mesoscopic Cooler Circuits (IMCC)
M. L. Philpott,* M. A. Shannon,* A. Fischer, J. Selby, D. Long
Defense Advanced Research Projects Agency

The project is developing a distributed system of lightweight, ultraefficient mesoscopic coolers that can be economically mass-produced to create a flexible refrigeration system. They are designed to transfer between 1 to 4 W of heat, over 40?C, with a COP from 4 to 7. The network of flexible, electrically powered IMCCs are approximately 120 mm (4.7 in.) square and 3 mm (< 1/8 in.) thick. The compressor is about the size of a quarter. The research involves developing innovative layered mesoscopic fabrication techniques including polymers and thin film layers with silicon-based electro-mechanical device fabrication.

MEMS Instructional Module for High School Students
T. Saif,* L. Benkowski, S. Tomasek, and E. Wiggins
National Science Foundation, ECS 97-34368

An instructional module is being developed on MEMS for high school students. The module will consist of a series of videotapes, a high school MEMS web page, and experimental MEMS demonstrations. The work is being conducted in collaboration with the University High School located on the University of Illinois campus.

Mesoscopic Thermomechanical (MTM) Water Purifier
J. G. Georgiadis,* M. A. Shannon,* D. He
Defense Advanced Research Projects Agency

The development of a new method for separating salts, nuclear, biological, and chemical contaminates from water. The method utilizes freezing fractionation and filtering with a novel thermomechanical desalinator and a new fiber filter.

Mesoscopic Thermomechanical (MTM) Water Purifier-An Energy-Efficient, Compact Approach to Cool, Filtered Drinking Water
J. G. Georgiadis,* M. A. Shannon, M. L. Philpott, J. Economy (Mater. Sci. & Engr.), J. Martel (CRREL), S. Maloney (USACERL), N. R. Miller, A. F. Vakakis
Defense Advanced Research Projects Agency

The objective of this project is to develop an energy-efficient, compact water purifier unit that can be employed by the military in the field. The proposed purifier exploits the physics of the mesoscale, in that performance improves as the size is reduced, and it spans the micro- to normal-scale. The mesoscopic thermomechanical (MTM) water purifier is based on classical physics on the micro- and meso-scale, and relies on a novel continuous fractionation process to remove high-concentration of ions and solutes in the water, followed by the use of optimized activated carbon fiber filters to retain nuclear, biological, and chemical contaminants (NBC).

Microengines Based on Combustion at the Microscale
M. A. Shannon,* R. I. Masel* (Chem. Engr.), G. Moore
DynCorp.

This exploratory research is aimed at developing the appropriate surface chemistries as well as material synthesis and fabrication to construct a microcombustor that will burn fuels without chemical and thermal quenching. The project seeks to test theory that suggests an approach to solving the quenching problems that currently keep microcombustion from occurring.

Microscale Thermal Sensing and Actuation Using MEMS
L. M. Phinney*
University of Illinois

MEMS, microelectromechanical systems, are a rapidly developing technology with applications in the automotive, health care, aerospace, environmental sensing, and consumer products industries. MEMS devices have been used to extend thermal measurement capabilities to greater sensitivities and smaller spatial resolutions than those achieved by traditional methods. Additionally, some MEMS devices are thermally actuated. For example, bimaterial cantilevers deform when heated because of mismatches in the thermal expansion coefficients and have been used to actuate MEMS devices. This project investigates using MEMS devices to measure heat transfer performance, thermophysical properties, and thermal actuation schemes.

Motion Amplification based Tunable, Bi-Stable, Low-Power Sensor Arrays
T. Saif*
University of Illinois

A new novel class of micromechanical sensors is being developed based on buckling of a long slender beam to sense a wide variety of physical parameters such as temperature, humidity, acceleration, and electromagnetic fields. The sensors have two stable equilibrium states. They change state when the physical excitation exceeds a threshold value. They consume power during state change only, not while maintaining the state. The nonlinear dynamical behavior of the sensors is studied, e.g., the response of the bi-stable system subjected to a white noise excitation (thermal noise).

Noninvasive Analysis and Manipulation of Single Cells Using MEMS Devices
T. Saif,* L. Allen* (Mater. Sci. & Engr.), M. B. Wheeler (Animal Sci.), C. Sager
National Science Foundation, ECS 98-07384

A single living embryo is mechanically probed using microactuators and sensors to study its internal fluid pressure, viscosity, mechanical stiffness, and dynamic response. The objective is to investigate whether these parameters change during cell division within the embryo. The study will reveal fundamental understanding of the biological processes during the initial stages of life. The parameters will also allow distinguishing between a healthy and a pathological embryo.

Refrigerant Flow through Small Orifices
C. W. Bullard,* P. S. Hrnjak,* X. Tu
Defense Advanced Research Projects Agency

Flow through small orifices (D=10-100mm) becomes a crucial issue in MEMS refrigeration systems. How do the cavity shape, surface roughness, and geometry at that scale affect the relationship between mass flow rate and the inlet thermodynamic state of the fluid? How do the governing equations differ from those applicable at microscale? These and other issues related to expansion device design are being addressed experimentally and analytically.

Reliability of Thermal Microactuators
T. Saif*
National Science Foundation, ECS 97-34368; Kodak

The project explores the primary mechanisms of thermomechanical fatigue and failure of MEMS thermal actuators made from metal-ceramic thin film layers. The medium of operation of these actuators may be vacuum, air, or liquids. MEMS sensors and actuators are used to understand the mechanisms of fatigue.