Production of hydrogen gas sensors based on sol–gel spin-coated Nb2O5 thin films

In the present work, single-layer and multi-layer Nb₂O₅ thin films were obtained by using sol–gel spin-coating technique and applying annealing temperature. The formation of hydroxyl on the Nb₂O₅ surface was determined by the FTIR technique. It is seen the structure turns into pure Nb₂O₅ form above 350 °C. Thickness effects on the structural and morphological properties of the annealed films were investigated by SIMS, XRD, XPS and AFM measurements. The thicknesses of the 1, 2 and 3-layered films are 65, 108 and 178 nm, respectively, and Nb₂O₅ films have amorphous structures even at an annealing temperature of 350 °C. RMS surface roughness of the films increased with increasing the film thickness increasing the stacked layers, while the 2-layered film has the highest surface area. After the characterizations have been defined, Ag interdigital electrodes were fabricated on the developed films with the Aerosol Jet Printing technique to produce H₂ gas sensors whose active material is single-layer and multi-layer Nb₂O₅ thin films. The sensing performances of the sensors were examined with respect to film thickness under H₂ concentrations ranging from 90 to 1200 ppm at operating temperature of 25 °C. Based on the 2-layered film, the sensor shows better hydrogen sensitivity, which can be at least partially caused by the higher surface area of the films and also associate with thickness of 108 nm. In addition, all fabricated sensors have good selectivity to H₂ gas compared to the other gases such as CO, O₂ and C₃H₈, as well as long-term stability over 90 days.