3 October 2003 In-plane optical measurement of vibrations of MEMS: gradient methods using interferometry and image processing
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Abstract
Optical probing is a non invasive tool useful to characterize the vibrations of the small moving components of microsystems (MEMS/MOEMS). This paper presents two complementary methods that can sense in-plane components of the vibration. The first one is a heterodyne interferometer, commonly used for out-of-plane component detection. The edge of the sample partially occults the laser beam, and, consequently, the intensity is amplitude modulated when the sample vibrates. The electronics has been modified so that both phase and amplitude of the output signal are extracted. Actual sensitivity is about 10-11 m/√Hz. In the second gradient method, a parallel acquisition of synchronous images is performed with a camera and a microcomputer, which stores the successive images for subsequent processing. Before digital lock-in processing, the images sequence is inter-correlated and interpolated to increase the accuracy of the method. This simple processing technique allows nanometer sensitivity. Both techniques are presented, analyzed and compared from theoretical and experimental point of view.
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Bernard Cretin, Bruno Serio, Pascal Vairac, "In-plane optical measurement of vibrations of MEMS: gradient methods using interferometry and image processing", Proc. SPIE 5145, Microsystems Engineering: Metrology and Inspection III, (3 October 2003); doi: 10.1117/12.500078; https://doi.org/10.1117/12.500078
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