Selective Detection of Toluene Using Pulse-Driven SnO₂ Micro Gas Sensors

Improvement of gas selectivity, especially among volatile organic compound (VOC) gases, was attempted by introducing pulse-driven modes in semiconductor gas sensors. The SnO2 microsensor was fabricated on a miniature sensor device constructed with a microheater and electrode. The gas-sensing properties were evaluated under a pulse-driven mode by switching the heater on and off. According to density functional theory calculations and temperature-programmed reaction measurements, toluene molecule, which is one of the VOC gases, was adsorbed on the SnO2 surface by van der Waals forces. The conventional sensor response, Se, defined as the change in the electrical resistance in air and target gas atmosphere, to toluene was four and eight times greater than that to CO and H2, respectively. Moreover, the newly proposed sensor response, Sp, defined as the change in the electrical resistance of the device in the target gas atmosphere during the heater-on period, to toluene was 33 and 29 times greater than that to CO and H2, respectively. This significant difference in the Sp to toluene was caused by the combustion reaction of condensed toluene within the sensing layer. Accordingly, the pulse-driven mode of the semiconductor gas sensor can be exploited to improve the gas selectivity of VOC gases based on these newly defined sensor response measures.