New In_xO_yN_z films for the application in NO₂ sensors

New gas-sensitive films of In_xO_yN_z have been fabricated by reactive rf-magnetron sputtering using an In₂O₃ target and an Ar/N₂ process atmosphere (0-65% N₂). The layers have been annealed for 10h at 600°C in synthetic air. Structural analysis (XRD, TEM, SEM, AES) shows that oxygen atoms are substituted by nitrogen atoms in the In₂O₃ lattice. An average nitrogen content of 1.9 at.% has been found by AES. Compared to pure In₂O₃ films, the In_xO_yN_z films show a completely changed morphology and microstructure with very small grains of 10-30nm arranged in a porous layer. The gas-sensitive behavior is enhanced significantly. The sensitivity towards various gases is increased and the response time τ₅₀ is reduced with increasing N₂ content in the sputtering atmosphere. The In_xO_yN_z layers sputtered using 65% N₂ exhibit the best gas-sensing properties. They show a very high NO₂ sensitivity of 38.7 ppm^-1 and a reduced response time of 5.9 min at 200°C where the pure In₂O₃ films are insensitive. At 400°C, the NO₂ sensitivity increases from 0.374 to 0.6 ppm^-1 and τ₅₀ is reduced from 10.5 to 2.8 min. The response time at 450°C is 1.2 min. A unique reversible dynamic behavior is found. The cross-sensitivity towards NH₃, CO, SO₂, H₂, and CH₄ is small. The In_xO_yN_z films have a high potential to be applied as new material for low-temperature conductivity NO₂ sensors.