Abstract-This paper identifies dynamic excitation parameters that promote decohesion of stiction-failed microcantilevers. The dynamic response of "s-shaped" adhered beams subjected to harmonic loading is described using modal analysis; this model is then used to predict the onset of debonding in the context of a critical interface energy. These theoretical results are used to rationalize preliminary experiments, which illustrate that dynamic excitation may be used to affect partial or complete repair of stiction-failed microcantilevers. The theoretical results provide fundamental insight regarding regimes where resonant effects trigger debonding and can serve as a potential mechanism for stiction repair. The models illustrate that driving a structure at resonance is usually beneficial with regards to debonding. However, this is not universally true; there is no benefit to driving a device at frequencies with unfavorable mode-shapes. Thus, these results provide a reasonable physical and mathematical explanation for the preliminary experimental results, while providing a roadmap for identifying parameters in future tests.[
Recently it has been shown that structural vibrations are an efficient means to repair stiction failed microcantilever beams. Experiments and analysis have identified excitation parameters (amplitude and frequency) that successfully initiated the debonding process between the microcantilever and the substrate. That analysis could not describe what happened after the debonding process was initiated. For example it could not predict if the beam would transition from a s-shaped to an arc-shaped configuration or even be repaired to a free-standing beam. The current research examines the post-initiation behavior of stiction failed microcantilever beams. A new-coupled fracture/vibration model is formulated and used to track the evolution of the repair in order to determine the extent of repair under various conditions. This model successfully explains phenomenological observations made during the experiments regarding the repair process being dependent on direction of frequency sweeps, complete and partial repair, and monitors the degree of repair no repair, partial repair or complete repair along with releases time associated with such repairs.
It has been shown in recent times that the use of structural vibrations is a viable approach in repairing stiction failed MEMS cantilever beams. It has also been observed that such a technique is sensitive to various parametric values associated with the de-sticking of these beams. In the current paper we present experimental results which characterize the ideal cantilever beam. An analytical model of stiction failed MEMS cantilever beams under electrostatic actuation is presented. Physical parameters such as stiffness, bending rigidity, damping, excitation voltage, etc. are incorporated in terms of Mathieu parameters to study the stability of the system. An experimental characterization of natural frequency, Young’s Modulus, and damping ratio, which form important components of the analysis, is presented. Accompanying these results is a description of the experimental set up used for finding these parameters. Experiments were performed at both atmospheric and vacuum pressures. An interferometric microscope mounted above the glass window of the vacuum chamber was used to determine the crack length of each beam and observe the profiles of the arrays of microcantilevers in-situ. A Laser Doppler Vibrometer was used for determination of characterization parameters. The microcantilevers were fabricated using the SUMMiT IV process of Sandia National Laboratories. Structural vibrations were induced by placing an alternating voltage on a cofabricated actuation pad located under the microcantilevers near their anchor point. Theoretical modeling shows the dependence of physical parameters that lead to stiction repair.
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