Optical EngineeringNew test methodology for static and dynamic shape measurement of MEMS
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Current trends in the miniaturization of structures require the use of smaller and smaller components. Development of these microcomponents and, in turn, of mechanical microstructures/microsystems requires, in addition to the integrated use of advanced design, analysis, and fabrication methodologies, state-of-the-art test and measurement methodologies. We have developed one such methodology, optoelectronic laser interferometric microscope (OLIM) methodology, with capabilities for rapid characterization of microelectromechanical systems (MEMSs). MEMSs are a unique class of mechanisms created using integrated circuit (IC) fabrication processes. Microgears and microengines, smaller than a gnat's eye, are groups of MEMSs created by such a process. MEMSs offer challenging opportunities for sensor/actuator applications and for improved test methodologies, e.g., shape measurement. This work has produced a new methodology for the characterization of MEMSs. To demonstrate the OLIM methodology, motions of a 64-µm-diameter microgear, driven at speeds up to 360,000 rpm, are investigated. Manufacturing tolerances result in gaps between the microgear and its hub. There gaps allow the microgear to tilt as it rotates. The OLIM methodology permitted measurements of tilt angles of less than 11 mrad, and deflections below 0.5 µm. Knowing how individual microgears behave is important, e.g., when many such gears are combined to form transmissions.