Fabrication of tin oxide nanowire gas sensors

Abstract

The diversification of gas sensing applications is motivated by society issues, such as environmental monitoring in industrialized cities, safety devices to prevent CO intoxication and indoor air quality control. Metal oxide gas sensors, which measure changes of the electrical resistance of the metal oxide due to the adsorption/desorption reactions of gas molecules on its surface at high temperature, exhibit high sensitivity to a broad range of flammable and toxic gases. Their success can be further explained by their simplicity and their low cost fabrication. Still, commercial metal oxide sensors, which are mainly based on tin oxide (SnO2) thick films, are rather bulky devices. The development of gas sensors based on metal oxide nanowires is promising regarding the improvement of the sensing performances, the miniaturization and the decrease of the power consumption of the devices. The aim of this thesis is to fabricate SnO2 nanowire sensors and to address the technological issues related to their fabrication. Therefore, the synthesis of SnO2 nanowires is developed based on a vapor growth method. Different materials (Al, Sn/Au, Cr/Au, Ti/Au and Au) are investigated to establish stable ohmic contacts with single SnO2 nanowires. The sensing properties of single nanowire sensors are characterized upon exposure to CO, H2 and H2S in dry and humid synthetic air at temperatures in the range 150-350°C. Preliminary results of nanowire sensors based on a suspended network of SnO2 nanowires, functionalized with metallic nanoparticles (Pd, Au or PdAu) or integrated on a suspended CMOS processed microhotplate are also presented.