NOx sensing properties of WO3-based semiconductor gas sensors fabricated by slide-off transfer printing

NO. sensing properties of semiconductor heterolayer sensors fabricated by slide-off transfer printing have been investigated. A WO3 single layer sensor showed much higher sensitivity to NO2 than that to NO. Loading of Ru or Pt on the surface Of WO3 led to a slight improvement of both the sensitivity and the response speed to NO, but the response speed to NO2 was decreased especially by the Ru loading. In contrast, loading of Au improved notably the sensitivities and the response behavior to both NO2 and NO. Stacking of a 0.5Pt-Al2O3 (0.5 wt% Pt-loaded Al2O3) layer over a 0.5Au-WO3 layer showed little effect on the NOx sensitivities, whereas double or triple stacking resulted in a remarkable enhancement of NO and NO2 sensitivities at 350degreesC. However, the NO2 sensitivity of these sensors was superior to the NO sensitivity. On the other hand, the NO2 sensitivity Of WO3 was decreased by the stacking of a Pt-Al2O3 catalyst layer, whereas the NO sensitivity increased. Such changes in NO sensitivity became more significant when the loading amount of Pt in the catalyst layer increased from 0.5 to 1.0 wt%. As a result, it was found that the 1.0Pt-Al2O3/WO3 heterolayer sensor exhibited comparable sensitivity to both NO2 and NO at 350degreesC.