Integration of Reactive Polymeric Nanofilms Into a Low-Power Electromechanical Switch for Selective Chemical Sensing

This paper presents the fabrication and demonstration of an ultrathin microelectromechanical chemical sensing device. Microcantilevers are etched from 100-nm-thick silicon nitride, and a 75-nm-thick reactive copolymer film for sensing is deposited by initiated chemical vapor deposition. Cross-linking densities of the polymer films are controlled during the deposition process; it is shown that greater cross-linking densities yield greater cantilever deflections upon the polymer´s reaction with the analyte. Considering that chemical reactions are necessary for stress formation, the sensing is selective. Cantilever deflections of greater than 3 ??m are easily attained, which allow a simple switch to be designed with resistance-based outputs. When exposed to a hexylamine vapor-phase concentration of 0.87 mol%, the resistance of the switch drops by over six orders of magnitude with a response time of less than 90 s.