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Title: Dynamic motion detection techniques for micromechanical devices and their application in long-term testing
Keywords: phonon, SEM, dynamic motion, micromechanical resonators, long-term testing, fatigue
Issue Date: 26-Aug-2010
Citation: WONG CHEE LEONG (2010-08-26). Dynamic motion detection techniques for micromechanical devices and their application in long-term testing. ScholarBank@NUS Repository.
Abstract: This thesis describes the development of two techniques for detecting nano-scale motion of micromechanical structures which can potentially be applied for long-term MEMS device testing. The first technique, acoustic phonon detection, utilizes mechanical waves or phonons generated by surface interaction or energy loss during device actuation to sense motion. Phonon detection has the unique capability of being able to provide insight into device mechanical state which is particularly useful for assessing long-term performance of MEMS devices. The technique is able to sense the vibration of state-of-the-art micromechanical resonators which exhibit sub-100 nm displacement. The second technique, stroboscopic scanning electron microscopy (SEM), is a high resolution imaging method that can capture the in-plane motion of MEMS devices down to 20 nm. Through secondary electron (SE) signal gating, it is possible to freeze the dynamic motion of a micromechanical structure and image it at its instantaneous position. The technique can further be applied to obtain a phase-resolved micrograph of the motion of the structure from which quantitative data, such as device displacement and velocity, can be derived. Both techniques were employed to investigate the long-term behaviour of comb actuated clamped-clamped beam resonators. Fifteen random samples were tested, each over a 500-hour actuation period, and the results indicate that the long-term frequency stability of the devices is dependent on the magnitude of axial stress on the beam structure. Three of the test samples exhibited possible signs of fatigue behaviour when their phonon dissipation properties were enhanced after several hundred hours of actuation. The enhanced dissipation gave rise to an increase in the magnitude of the phonon voltage generated per nm of resonator displacement. Such a change in the mechanical characteristics (i.e. phonon dissipation) of the device cannot be identified by current electrical testing methodologies.
Appears in Collections:Ph.D Theses (Open)

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