Humidity sensing properties of WO3 thick film resistor prepared by screen printing technique

Thick films of tungsten oxide based were prepared using standard screen printing technique. To study the effect of temperature on the thick films were fired at different temperature for 30 min in air atmosphere. The WO3 thick films were characterized with X-ray diffraction, scanning electron microscopy and EDAX for elemental analysis. The formation of mixed phases of the film together with majority of monoclinic phase was observed. IR spectra confirm the peak at 1643 cm−1 clearly shows stretching vibrations attributed to the WOH bending vibration mode of the adsorbed water molecules. The absorption peaks in the range 879-650 cm−1 are attributed to the stretching WOW bonds (i.e. ν [WOinterW]). The peak located at 983 cm−1 belong to WO terminal of cluster boundaries. A change in the resistance was observed with respect to the relative humidity when the WO3 thick films were exposed to a wide humidity range of 20-100%. An increasing firing temperature of WO3 film increases with the sensitivity. The parameters such as sensitivity and hysteresis of the WO3 film sensors have been evaluated.