Transparent conducting oxide electrodes for novel metal oxide gas sensors

Abstract

We report fabrication and gas sensing properties of semiconducting metal oxide gas sensors using conducting oxide electrodes. Indium-tin oxide (ITO) and aluminum-doped zinc oxide (AZO) films are used to replace Pt electrodes in WO3 or SnO2 thin-film gas sensors. Before and after thermal annealing at 300 degrees C for 3200 min, the resistivity of the ITO film increases from 1.3 x 10(-4) to 7.0 x 10(-4) Omega cm, whereas the AZO film shows a significant increase in resistivity from 2.0 x 10(-3) to 5.1 x 10(1) Omega cm due to the annihilation of oxygen vacancies in the film. Upon exposure to 50 ppm CO at 300 degrees C, WO3 or SnO2 thin-film sensors with ITO interdigitated electrodes (IDEs) on glass substrates display higher responses than sensors with Pt IDEs, attributed to the low-resistance ohmic contacts between the electrode (ITO) and the sensing material (WO3 or SnO2). The reproducible response, the concentration-dependent modulation in sensitivity, and a sub-ppm detection limit indicates the reliable operation of sensors made with ITO IDEs. The high transmittance, exceeding 75%, of the sensors at visible wavelengths holds promise for future applications to transparent gas sensors. (C) 2011 Elsevier B.V. All rights reserved.