Influence of the poly(vinyl butyral) binder in screen-printed thick-film gas sensors containing NiO-TiO2 oxides

This study investigates gas sensitive resistors fabricated by screen-printing inks created from a mixture of NiO-TiO2 and containing a poly(vinyl butyral) binder for the detection of alcohol vapors at room temperature. It was found that these films exhibited a significant resistance change in response to the vapors, while also displaying an inherent selectivity, proving most sensitive to toluene and propanol vapor; with comparatively low responses exhibited towards ethanol and methanol vapors. It is proposed that swelling of the polymer binder used in the fabrication of the NiO-TiO2 thick-films, rather than oxygen ion induced majority carrier modulation in the oxides, is the significant factor in causing the electrical resistance of the films to increase upon exposure to the organic solvent vapors. Very fast response and recovery times of 9 s and 16 s, respectively were recorded for the devices upon exposure to 4000 ppm step changes in propanol concentration. For comparative analysis, poly(vinyl butyral)/carbon black composites were fabricated from a by a drop-coating technique. The superior sensitivities and response times of the screen-printed sensors were attributed to the (SEM confirmed) highly porous structure attained by the thick-film devices, caused by the excessive free-volume induced in the polymer-binder matrix by the oxide materials. The results suggest that the effects of the polymer binder, even when present in comparatively small amounts, cannot be ignored in certain sensing applications.