New InxOyNz films for the application in NO2 sensors

New gas-sensitive films of InxOyNz have been fabricated by reactive rf-magnetron sputtering using an In2O3 target and an Ar/N-2 process atmosphere (0-65% N-2). The layers have been annealed for 10 h at 600 degreesC 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 InxOyNz films show a completely changed morphology and microstructure with very small grains of 10-30 nm arranged in a porous layer. The gas-sensitive behavior is enhanced significantly. The sensitivity towards various gases is increased and the response time tau (50) is reduced with increasing N-2 content in the sputtering atmosphere. The InxOyNz layers sputtered using 65% N-2 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 degreesC where the pure In2O3 films are insensitive. At 400 degreesC, the NO2 sensitivity increases from 0.374 to 0.6 ppm(-1) and tau (50) is reduced from 10.5 to 2.8 min. The response time at 450 degreesC is 1.2 min. A unique reversible dynamic behavior is found. The cross-sensitivity towards NH3, CO, SO2, H-2, and CH4 is small. The InxOyNz films have a high potential to be applied as new material for low-temperature conductivity NO2 sensors. (C) 2001 Elsevier Science B.V. All rights reserved.