The success of many advanced technologies that use devices such as sensors and actuators, including gyroscopes and optical devices, depends on microscopic components called microelectromechanical systems (MEMS) devices made of polycrystalline silicon (polysilicon). Researchers at Case Western Reserve University report in the November 8 issue of Science that miniature micron-sized polysilicon laboratory specimens subjected to cyclic tension/compression loading undergo fatigue, and could ultimately fail as a result of damage produced by the compressive cycles, rather than from moisture-assisted stress corrosion cracking. This information, they say, could assist MEMS developers to mitigate fatigue failure in MEMS devices that experience significant mechanical stress during operation.
The Science article ("Fatigue Failure in Polysilicon: It’s Not Due to Simple Stress Corrosion Cracking") was written by Harold Kahn, Research Associate Professor in the department of materials science and engineering; Roberto Ballarini, Professor in the department of civil engineering and a lead researcher on the project; Arthur Heuer, University Professor and Kyocera Professor of Ceramics in the department of materials science and engineering; and Justin Bellante, a recent BS/MS graduate of materials science and engineering.
Polysilicon, CWRU researchers say, is a manufactured thin film consisting of silicon crystallites that is made in a microfabrication laboratory using chemical vapor deposition. The films are associated with rough surfaces that result from the plasma etching used in the final stages of MEMS processing. The researchers speculate that under compressive loading, these surfaces come into contact, and their wedging action produces microcracks that grow during subsequent tension and compression cycles.
Marci E. Hersh | EurekAlert!
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