Investigating the influence of Al-doping and background humidity on NO₂ sensing characteristics of magnetron-sputtered SnO₂ sensors

Elevated temperatures and humidity contents affect response, lifetime and stability of metal-oxide gas sensors. Remarkable efforts are being made to improve the sensing characteristics of metal-oxide-based sensors operating under such conditions. Having versatile semiconducting properties, SnO2 is prominently used for gas sensing applications. The aim of the present work is to demonstrate the capability of the Al-doped SnO2 layer as NO2 selective gas sensor working at high temperatures under the presence of humidity. Undoped SnO2 and Al-doped SnO2 (3 at. % Al) layers were prepared by the radio frequency (r.f.) reactive magnetron sputtering technique, having an average thickness of 2.5 μm. The sensor response of Al-doped SnO2 samples was reduced in the presence of background synthetic air. Moreover, under dry argon conditions, Al doping contributes to obtain a stable signal and to lower cross-sensitivity to CO in the gas mixtures of CO + NO2 at temperatures of 500 and 600 °C. The Al-doped SnO2 sensors exhibit excellent chemical stability and sensitivity towards NO2 gas at the temperature range of 400–600 °C under a humid environment. The sensors also showed satisfactory response (τres = 1.73 min) and recovery (τrec = 2.7 min) towards 50 ppm NO2 in the presence of 10 % RH at 600 °C.