Unique detection of organic vapors below their auto-ignition temperature using III-V Nitride based triangular microcantilever heater

We report on the unique detection of dilute volatile organic compounds below their auto-ignition temperature using a novel AlGaN/GaN heterostructure based triangular microcantilever heater. With a low input power of 12 mW, the microcantilever heater was found to reach a maximum temperature of 330 °C at the tip, which was verified through infrared microscopy and Raman spectroscopy. Unique threshold voltages were observed for various organic analytes with different functional groups, beyond which the heater current started to increase sharply in presence of analytes, which correlated strongly with their latent heat of evaporation. Dilute vapors with concentrations as low as 50 parts per million (ppm) could be detected selectively with a noise limited resolution down to 5 ppm. On the other hand, the magnitude of change of current for a fixed applied voltage was found to be dependent on the molecular dipole moment of the analytes, which can likely be attributed to the strong surface polarization of AlGaN. A simple circuit model has been proposed to explain the observations. Heat transfer and Joule heating simulations were performed using finite element method to model the electro-thermal characteristics of the microcantilever heater, which were in good agreement with the experimental observations.