Polymer Coated Tin Oxide Nanowires for Improved Sensitivity of MEMS Chemical Sensors Based on Microbeams

MEMS mass sensors are an important field of study for chemical and biological sensing. We utilize the massive surface area to volume ratio of tin oxide nanowires to improve the sensing characteristics of resonant cantilever gas sensors. The nanowires are grown onto released silicon cantilevers via the vapor liquid solid method, a type of chemical vapor deposition. Through intelligent catalyst placement the nanowires are grown selectively onto predefined surfaces of the cantilever. The increased surface area of our nanowire coatings provides greatly increased active binding area for analytes, while high quality factors are still achieved with this method. Our experiments actively monitor the removal of a silane self assembled monolayer from the sensor surface. Current nanowire coated sensors show a tenfold increase in sensitivity when compared to the bare sensors. We have functionalized the nanowires with a variety of polymer coatings. These functionalized sensors also show a substantial increase in sensitivity to the analytes. By varying the polymer coating applied to the nanowires, a sensor array can be generated that achieves gas recognition while having incorporated the increased sensitivity of the nanowire coatings.