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Si nanowire (NW) stacks are fabricated by utilizing the scalloping effect of inductively coupled plasma deep reactive ion etching. When two etch windows are brought close enough, scallops from both sides will ideally meet along the dividing centerline of the windows turning the separating material column into an array of vertically stacked strings. Upon further thinning of these NW precursors by oxidation followed by oxide etching, Si NWs with diameters ranging from 50 nm to above 100 nm are obtained. The pattern of NWs is determined solely by photolithography. Various geometries ranging from T-junctions to circular coils are demonstrated in addition to straight NWs along specific crystallographic orientations. The number of NWs in a stack is determined by the number of etch cycles utilized. Due to the precise lithographic definition of NW location and orientation, the technique provides a convenient batch-compatible tool for the integration of NWs with MEMS. This aspect is demonstrated with a microgripper, where an electrostatic actuation mechanism is simultaneously fabricated with the accompanying NW end-effectors. Mechanical integrity of the NW-MEMS bond and the manipulation capability of the gripper are demonstrated. Overall, the proposed technique exhibits a batch-compatible approach to the issue of micronanointegration.
Date of Publication: Dec. 2009