Response Times of Metal-Oxide Chemiresistors: Comparison Between the Isothermal and Temperature Modulation Modes

The response time is one of the main functional parameter for gas sensors, including metal oxide chemiresistors. This parameter is widely investigated for devices working in isothermal mode but it is much less investigated for gas sensors working in temperature modulation mode. In this work, considering ethanol as target gas, we compare the response times of a metal oxide chemiresistor working according to these two modes. In order to compare them, we worked with nearly the same average temperature in both cases, supplying a constant voltage to the heater in the isothermal mode and a squared voltage wave in temperature modulation. Our results show that, depending on the average working temperature, one mode or the other may be faster. At high average working temperature, the response time recorded with the isothermal mode is shorter than the thermal-period of the temperature modulation mode. Lowering the average working temperature, the response time increases for both modes, but the increase is more marked for the isothermal mode, which become slower than the temperature modulation one.