Seminar Series - 2000-2001

Tensile Testing of MEMS Materials

W. N. Sharpe, Jr.
Professor, Department of Mechanical Engineering
Johns Hopkins University

Sponsored by: Center for Materials Research and Analysis and a grant provided by Professor Emeritus C. Wayne Martin

Date: Tuesday, September 26, 2000
Time: 3:30 p.m.
Place: W128 Nebraska Hall


Microelectromechanical systems (MEMS) are tiny devices fabricated by techniques commonly used in the microelectronics industry, and they incorporate a mechanical element into a sensor or actuator. Examples are accelerometers used in automobile airbag systems, disposable pressure transducers used in intensive care units, and mechanical locks for munitions. The mechanical components are either very thin and small (dimensions on the order of microns) as in polycrystalline silicon or larger (tens of microns) as in electroplated nickel.

These are actually new materials because the manufacturing processes are different than those for common structural materials, and their mechanical properties must be known for accurate design and life prediction. Tensile testing is the standard approach for mechanical testing of materials, but there are three main challenges in testing such small specimens – handling, friction, and strain measurement.

Nickel tensile specimens 200 microns thick are deposited in the shape of a dog biscuit on a silicon substrate. They can be released by etching and the wedge-shaped ends placed in matching grip inserts. Friction is reduced via a linear air bearing and strain is measured by interferometry between reflective indentations in the center portion of the specimen. The very thin polysilicon specimens are fastened to a silicon substrate at one endwith the other end being gripped with an electrostatic probe. Strain is measured interferometrically from two gold lines deposited on the specimen. Techniques and procedures will be described for both kinds of materials and the latest results will be presented.


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