Low-temperature hydrogen sensor based on sputtered tin dioxide nanostructures through slow deposition rate

In this paper, tin dioxide (SnO2) mesoporous nanostructures (pores of 2 and 50 nm) were directly sputtered on a Pt-interdigitated electrode (gap length of 35 μm) with a slow deposition rate of 5 nm/min under a controlled substrate temperature of 100, 350, and 500 °C. It is found that the surface area was 0.22 × 104, 0.18 × 104, and 0.17 × 104 observed for the nanostructure prepared at 350 °C, 500 °C, and 100 °C, respectively. The film crystallinity increased with increasing the substrate temperature. The film prepared at 500 °C showed a lower resistivity in air. Most importantly, the sensor fabricated by using the nanostructure prepared at 500 °C exhibits excellent low-temperature (100 °C) H2 sensing properties. When this sensor is exposed to 1000 ppm (0.1%) H2, the sensor response is 30 × 103 %. The sensing performances are superior to those of most reported at higher temperature H2 sensors based on SnO2 materials. Interesting is the sensor selectivity, where the sensor prepared at 500 °C is selective toward H2 gas, while the sensor prepared at 350 °C is selective toward NO2 gas. The sensing performance of the sensor prepared at 500 °C for H2 (reducing gas) was attributed to a proposed mechanism of a coulomb interaction (electric dipole). The sensors exhibit two different behaviors of their electrical resistivities upon exposure to H2 gas at low and high temperatures. The gas sensing mechanisms for such behaviors were proposed to understand the sensor behavior. The current results may assist in realizing high selective sensors toward H2 for the commercial market.