Full-Field Digital Holographic Vibrometry for Characterization of High-Speed MEMS
Development of quantitative full-field high-speed imaging modalities are indispensable to monitor the real-time transient performance of Micro-electromechanical Systems (MEMS). Their performance is a direct result of how devices are designed and fabricate
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Full-Field Digital Holographic Vibrometry for Characterization of High-Speed MEMS Payam Razavi, Cosme Furlong, and James D. Trolinger Abstract Development of quantitative full-field high-speed imaging modalities are indispensable to monitor the real-time transient performance of Micro-electromechanical Systems (MEMS). Their performance is a direct result of how devices are designed and fabricated and any imperfection in either of them renders undesirable results. Furthermore, new devices are being designed to comply with tighter geometrical tolerances while operating at higher speeds. In this paper, we report progress in the development of a new High-speed Digital Holographic System (HDHS) for characterization of nanometer scale transient (i.e., >100 kHz) displacements of MEMS in full-field. Comparisons of the results obtained with our HDHS and those obtained with Laser Doppler Vibrometery (LDV) indicate a high level of correlation, which validates the measuring capabilities of our developed system. The high temporal and spatial (i.e., microseconds at >100k data points) resolutions of our HDHS enable concomitant measurements at all points to quantify spatially dependent motion parameters, including modal frequencies, time constants, Q-factors, changes in shapes, and surface strains. Representative results of the study of a high-speed MEMS deformable mirror are presented to show the capabilities of our method. Keywords Digital high-speed holography • Full-field measurements • MEMS testing • Transient response
4.1
Introduction
It is estimated that up to 80 % of the fabrication costs of many MEMS involve final packaging and testing [1], which are critical for the development of reliable devices. In addition, as new MEMS devices operate at unprecedented speeds, suitable tools to measure their performance become an essence. The need for high-speed full-field measurements is mostly due to the following factors: • Unknown transient performance of MEMS devices under variations of environmental conditions such as surrounding medium, pressure, orientation, and temperature [2]. • Accuracy and performance of new devices require quantitative measurements as a feedback to their design and fabrication. In the case of kinematics of high-speed MEMS (i.e., >5 kHz), current operational MEMS testing devices such as Laser Doppler Vibrometry lack full-field capabilities with sufficient spatial resolutions. In addition, other testing methods to study kinematics of MEMS, such as stroboscopic holographic interferometry, require multiple measurements and characterization of the transient response of MEMS becomes difficult [3]. In this paper, we report advances in the development and application of a High-speed Digital Holographic System (HDHS) with the measuring capabilities that include high-measuring range (i.e., from nanometers to micrometers), fullfield-of-view (i.e., >140,000 points), and high-speed (i.e., >40 kHz). Our methods, unlike others, have the unique capability of utilizing the full spatio-temporal resolution of high-speed
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