Transient response of resistive-type NO2 sensor on temperature change

The transient resistance response of a SnO2 sensor after an abrupt temperature change was measured, and consequently peculiar responses of the sensor in NO2 gas were observed. SnO2 thick film sensors, with a thickness of approximately 10 mum, were prepared by a conventional screen printing method. The films were printed on interdigitated Pt electrodes deposited on the front side of an Al2O3 substrate and a Pt heater was deposited on the backside of the substrate. Gas-sensing measurements were carried out using 20% O-2/N-2 with a few ppm NO2 gas flow. The temperature of the sensor was changed in steps of 100 degreesC from 100 to 400 degreesC, and kept constant for 2 min at each step using an electronic control circuit. A reference sensor fabricated in ZnSb2O6 was also prepared and measured by the same method. In addition, the adsorption and desorption characteristics of the gas-sensing material for NO2 were examined by doing temperature programmed desorption (TPD) measurements. The resistance decreased as the temperature increased, and increased when NO2 was present. The transient response in NO2 had a peaked point between 200 and 300 degreesC. On the other hand, no peak response was observed for the ZnSb2O6 sensor. As seen from the TPD measurements, the desorbed NO2 from SnO2 was much higher than that from ZnSb2O6, therefore, the peak response of the SnO2 sensor seems to be related to the adsorption and desorption properties of the gas-sensing material. (C) 2003 Elsevier Science B.V. All rights reserved.