Gas sensing properties of SnO2 single nanowire transistors

In the last decades there has been an increasing interest on the applications of oxide semiconductors as gas sensors. Tin oxide (SnO2) is the most used material due to its high sensitivity and stability at lower operational temperature. SnO2 gas sensors have been usually fabricated in the form of thin films. These gas sensors demonstrated an acceptable level of sensitivity but the response is relatively slow because it takes significant time for a target gas to infiltrate into the SnO2 particles and adsorb on the surface. Recently, nanostructures like nanowires and nanobelts have gained considerable attention due to their huge surface-to-volume ratio, which makes them ideal candidates for chemical sensing applications. Here we present the fabrication and characterization of single nanowire (SNW) gas sensors, both passive (resistor) and active (field effect transistor). The SnO2 nanowires are grown by CVD, while the bottom-gate, top-contact configuration, is achieved via standard lithographic techniques. The sensor performance of the SNW devices (optimal working temperature, sensitivity, response and recovery time) are investigated as a function of the nanowire diameter, in the range 60-120 nanometers. The single nanowire sensors show good sensitivity and a very fast response time (few seconds) compared to multiple nanowire devices, even at low temperature. Therefore, this approach proves to be the natural candidate for real-time sensing applications.