A route to high sensitivity and rapid response Nb2O5-based gas sensors: TiO2 doping, surface embossing, and voltage optimization

We report a novel route for the fabrication of highly sensitive and rapidly responding Nb2O5-based thin film gas sensors. TiO2 doping of Nb2O5 films is carried out by co-sputtering without the formation of secondary phases and the surface area of TiO2-doped Nb2O5 films is increased via the use of colloidal templates composed of sacrificial polystyrene beads. The gas sensitivity of Nb2O5 films is enhanced through both the TiO2 doping and the surface embossing. An additional enhancement on the gas sensitivity is obtained by the optimization of the bias voltage applied between interdigitated electrodes beneath Nb2O5-based film. More excitingly, such a voltage optimization leads to a substantial decrease in response time. Upon exposure to 50 ppm CO at 350 °C, a gas sensor based on TiO2-doped Nb2O5 film with embossed surface morphology exhibits a very high sensitivity of 475% change in resistance and a rapid response time of 8 s under 3 V, whereas a sensor based on plain Nb2O5 film shows a 70% resistance change and a response time of 65 s under 1 V. Thermal stability tests of our Nb2O5-based sensor reveal excellent reliability which is of particular importance for application as resistive sensors for a variety gases.