The influence of nanoscale atomic-layer-deposited alumina coating on the fatigue behavior of polycrystalline silicon thin films

The influence of atomic-layer-deposited alumina surface coatings on the fatigue of polycrystalline silicon thin films was investigated. Tests were performed on 2-mu m-thick notched cantilever-beam structures actuated at resonance (similar to 40 kHz) that were coated with similar to 20 nm of alumina deposited at 100 degrees C. The coated devices show a drastically different frequency evolution behavior as compared to uncoated specimens, while no surface oxide thickening during cycling is observed in bright-field transmission electron microscopy. Both results are consistent with a surface degradation mechanism for polycrystalline silicon fatigue such as the reaction-layer mechanism. The improved frequency evolution has the potential of increasing the performance of resonator-based microelectromechanical system sensors.