Detection of nanogram explosive particles with a MEMS sensor

MEMS (microelectromechanical systems) technology was used to fabricate arrays of sensors for detecting the explosive micro particulate residue found in mine fields. MEMS devices were fabricated by a surface micromachining process provided by MCNC. The sensor consists of a bimorph structure of polysilicon/gold cantilevers. An optical detection system was designed to detect the deflection of the cantilevers. The sensors were heated by either radiation or conduction using an UV lamp and a small heater under the sensor chip respectively. The deflection of the cantilevers with increasing temperature is presented. Experiments have been performed to detect the response of the cantilevers in the presence of: an explosive particle. The cantilevers show a response due to the presence of nanograms of TNT and RDX in the vicinity of the cantilevers. Currently it is understood that the response shown by the cantilevers is due to the vaporization of the micro particles, which pulls significant heat out of the temperature sensitive beams causing detectable beam motion. The chemical selectivity of the sensor is provided by the unique melting temperatures of TNT and RDX.