Nanoporous SnO[sub 2] Film Gas Sensor Formed by Anodic Oxidation

Nanoporous SnO 2 films on SiO 2 /Si substrate with one-dimensional (1D) nanochannels were fabricated by anodic oxidation, and their gas sensing properties were investigated. For this, Sn films of ~600 nm thick were deposited on SiO 2 /Si substrate by thermal evaporation and anodized in an electrolyte of 0.3 M oxalic acid. Subsequent annealing at 700°C completely transformed amorphous anodic oxide into crystalline SnO 2 , which was confirmed by X-ray diffraction. During annealing, both 1D nanoporous structure and adhesion to the substrate were maintained. The pore shape was more or less spherical, and the channel diameter and wall thickness were ∼50 and ∼20 nm, respectively. The Pt-patterned nanoporous SnO 2 film sensor responded to H 2 , NH 3 , and CO gases with a relatively short response time. It showed the highest gas response (S) of ∼52 toward 1.0% H 2 /air at 400°C and exhibited the linear concentration dependence and high selectivity toward H 2 against CO or NH 3 . The sensing performance of the nanoporous SnO 2 film sensor was compared with that of the thermally oxidized SnO 2 film sensor without the anodizing step and commercial SnO 2 powder sensor.