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Integration of Reactive Polymeric Nanofilms into a Low-Power Microelectromechanical Switch

Wyatt E. Tenhaeff1, William J. Arora2, George Barbastathis3, and Karen K. Gleason1. (1) Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 66-419, Cambridge, MA 02139, (2) Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, (3) Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139

An ultrathin microelectromechanical switch with integrated reactive polymeric nanofilms has been fabricated and demonstrated for selective chemical sensing. Microcantilevers were etched from 100 nm thick silicon nitride membranes and were coated with 75 nm of crosslinked copolymer films via initiated chemical vapor deposition. Two crosslinking densities were compared; it was shown that the higher crosslinking densities yield greater cantilever deflection upon the reaction of the polymer with analytes. Volumetric confiments imposed by crosslinking were thought to be responsible for the greater stress. Deflections of greater than 50 µm enabled the design of the switch with simple electrical resistance-based outputs. Upon exposure to a hexylamine vapor-phase concentration of 0.9 mol%, the resistance dropped by over six orders of magnitude in less than 90 seconds. The sensor does not respond to nitrogen vapor saturated with heptane or isopropanol, showing that chemical reaction is necessary for signal transduction. In the “off” state, the switch is open and draws negligible power.

Multiple polymer chemistries have been investigated, and potential defense applications for the sensor will be discussed. Furthermore, alternative device designs will be described.