Response model for thermally modulated tin oxide-based microhotplate gas sensors

To gain some insight into the conductance response of temperature-modulated metal oxide gas sensors, we introduce a model for the physicochemical processes involved in the sensing operation. For this, we consider the interactions that take place at the sensor surface in the presence of reducing and oxidising species. Then we validate the model against experimental responses in the presence of ppm levels of CO and NO2 in air. A sinusoidal voltage drives a resistive platinum heater and modulates the temperature of a micromachined tin oxide gas sensor; the resulting variation in conductance is analysed. Excellent agreement between theoretical and experimental responses is achieved. The model developed was used to compute the conductance response of a temperature-modulated sensor in the presence of different concentrations of CO and NO2. Features from the simulated response transients were extracted using the discrete wavelet transform and classified using a principal component analysis. A linear separation between CO and NO2 was obtained, which is in good agreement with our previous experimental results. (C) 2003 Elsevier B.V. All rights reserved.