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17 June 2009 Dynamic evaluation of lateral and vertical displacement of thermally actuated MEMS devices
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Scanning white light interferometry (SWLI) allows dynamic full-field 3D profiling of MEMS devices. With stroboscopic illumination periodic out-of-plane oscillation can be characterized, but in-plane movement is unresolved. We combine stroboscopic SWLI with image processing to concurrently characterize periodic out-of-plane and in-plane displacement. A difference in frequency is induced between the sample excitation and stroboscopic illumination signals. The difference frequency is chosen to allow recording the surface movement at video rate. The stroboscopic image is thus no longer frozen in time, but moves at frequency equal to the difference in stroboscopic frequencies. This motion is captured with a CCD camera. The surface velocity is extracted from the apparent motion using optical flow algorithms. For concept validation we characterize the in-plane and out-of-plane movement of thermal microbridges fabricated on silicon-oninsulator by deep reactive ion etching. The microbridge geometry was designed for in-plane movement with minor outof plane deflection.
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Kalle Hanhijärvi, Juha Aaltonen, Ivan Kassamakov, Lauri Sainiemi, Kestutis Grigoras, Sami Franssila, and Edward Hæggström "Dynamic evaluation of lateral and vertical displacement of thermally actuated MEMS devices", Proc. SPIE 7389, Optical Measurement Systems for Industrial Inspection VI, 73892Z (17 June 2009);

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