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Title: Thermal Modulation of Microfabricated Cantilever-based Chemical Sensors for Improved Selectivity
Committee:
Dr. Oliver Brand, ECE, Chair , Advisor
Dr. Levent Degertekin, ECE
Dr. Fatih Sarioglu, ECE
Dr. Azadeh Ansari, ECE
Dr. Todd Sulchek, ME
Abstract:
This work investigates the integration of heaters on a polymer-coated, mass-sensitive resonant cantilever for gas-phase chemical detection of volatile organic compounds. Integrated diffused resistors modulate the temperature of the polymer film, and the analysis of sorption kinetics at the elevated temperatures is used to discriminate between similar analytes. Multiple polymers are tested as an absorbing layer to determine suitability for analyte identification with this new technique. Heating pulses of various amplitudes, applied to the diffused resistors, raise the film temperature by 3-30 °C. Measuring the steady-state frequency shift of these mass-sensors as a function of temperature can improve the selectivity of the coated polymeric sensing film by extracting characteristic analyte properties that can aid in analyte discrimination. This analysis successfully estimates the vaporization enthalpies of the tested analytes with an average error of 1% for an OV-1 coating, as one metric for analyte identification. Additionally, various methods are explored to increase the selectivity of the sensor via analyzing the transient response of analyte absorption and desorption at various temperatures and heating schemes. Both the steady state and transient responses are used in supervised machine learning techniques to differentiate between similar analytes. Pursuant to these tasks, this also work demonstrates improved frequency stability, in the presence of environmental variations, through decreases in the Allan deviations, thus, improving the limits of detection (665 ppb for benzene, 158 ppb for toluene and 41 ppb for o-xylene).
