On the effects of the materials and the noble metal additives to NO2 detection

Using screen-printing techniques, sensitive layers of tungsten and tin oxide were deposited on silicon micromachined substrates. The goal sought with this study was the fabrication of highly sensitive NO2 sensors. For this purpose, the response of the different sensitive layers to NO2 and other interfering species like ethanol, ammonia and carbon monoxide was studied at different operating temperatures. The deposition of active layers was made before the membranes had been etched, which avoids damages during film deposition. The microstructure of the sensitive films is analyzed by means of SEM and EDX. The effect of the active layer material (WO3 and SnO2), the noble metal additives (Au, Pt or Pd) and their quantity (1, 2 and 4 wt.%) was fully studied.