Near-zero curvature fabrication of miniaturized micromechanical Ni switches using electron beam cross-linked PMMA

Abstract

We report on the fabrication and characterization of one of the smallest near-zero curvature nickel cantilevers, acting as part of a three-terminal electrostatically actuated switch across a nanoscale gap. A surface nanomachining technique using electron beam cross-linked polymethylmethacrylate (PMMA) as the sacrificial layer combined with nickel electroplating as the structural material is developed. Sharper contact bumps were realized via reflow of PMMA resist, with tunnel junctions formed by the in situ formation of aluminium oxide during the oxygen plasma dry release step. Preliminary results show that a 0.21 μm thick plated nickel cantilever beam with dimensions of 10 μm by 4 μm suspended over a 0.43 μm gap demonstrates low hysteretic behaviour (∼2.5 to 3 V) and a pull-in voltage of 27.5 V. No significant plastic deformation of the curl-free cantilevers was evident even after 1 billion switching cycles. Simple current detection techniques through a resonating cantilever-driver system are used to detect motion of the structures with resonant frequencies above 2 MHz. Because of its reliable curl-free properties, switching performance is stable and repeatable. This should pave the path towards flat nanoelectromechanical systems (NEMS) to enable both basic and applied research.