Reliability study of AlN-driven microcantilevers based on interferometric measurements of their static and dynamic behaviours

Microelectromechanical systems (MEMS) are exposed to a variety of environmental conditions, making the prediction of operational reliability difficult. In this contribution, we investigate the environmental effects on the static and dynamic properties of piezoelectrically actuated MEMS microcantilevers where aluminium nitride (AlN) is used as actuation material. The environmental effects to be considered include thermal and humid cycling, as well as harsh electrical loading performed under standard weather conditions. Investigated properties are defined for the static behaviour (i.e. determined initial deflection, out-of-plane displacement vs. constant voltage) and dynamic behaviour (i.e. determined 1st resonance frequency, vibration amplitude at 1st resonance mode) of AlN-based microcantilevers. The metrology tool is a Twyman Green interferometer, operating in both stroboscopic regime and time-average interferometry mode. The initial deflection and the frequency changes of the first resonance mode of microcantilevers are monitored during the accelerated thermal aging, the humidity tests, as well as harsh electrical loading and fatigue tests. Finally, the resonant fatigue tests, accelerated by application of a high voltage are accomplished to evaluate the lifetime of microcantilevers. For constant values of voltage higher than 15 V, a delamination of top electrode of AlN transducer is observed.

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