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 [micro]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. [2008-0132] Index Terms--Chemical-vapor deposition (CVD), microsensors, thin films, three-dimensional nanomanufacturing.