Self-adapted temperature modulation in metal-oxide semiconductor gas sensors

Sensing mechanisms of gas sensors depend on temperature, and this is in particular true for metal-oxide semiconductors where the peculiar role of temperature suggested the modulation of temperature as a viable method to tune selectivity and sensitivity. This principle was widely investigated in the past, and methods to design ad hoc temperature behaviors have been proposed. In this paper, instead of a priori temperature profiles, a self-adaptive temperature modulation is proposed. For the scope, a closed-loop circuit connecting the sensor resistance to the sensor heater is designed. In this condition changes in sensor resistance are reflected into changes of operating temperature. Herewith, the method is implemented with an oscillatory circuit, so with a steady resistance value the signal driving the temperature modulation converges to a periodic pattern of pulses that is specific for the sensor state. Since the relationship between resistance and temperature may depend on the quality and quantity of the gas at which the sensor is exposed, the temperature modulation signal is likely dependent on the kind of gas and its concentration. As a consequence, features describing the temperature modulation signal pattern can be used as a multicomponent variable that can allow for gas identification and quantification. The hypothesis is confirmed by simulations with electronics CAD software and experiments with a commercial metal-oxide semiconductor gas sensor. Results show that optimal gas identification and concentration are simultaneously possible with a unique sensor device.