Fine-tuning of gas sensitivity by modification of nano-crystalline WO3 layer morphology

The effect of WO3 nano-crystal characteristic size and layer morphology on gas sensitive properties was investigated in order to define the optimum preparation process. WO3 layers were synthesized by hydrothermal acidic precipitation method using different chemicals and reactive sputtering as reference. Micro-hotplate based conductivity type devices were fabricated and the sensitivity on NH3 up to 100 ppm was measured in the temperature range of 140-240 °C. The measurements revealed that the characteristic size of the WO3 nano-crystal plays primary role, but layer morphology opens the way towards extended measuring range. The nano-rod structures operated at 220 °C exhibit the best sensing characteristics in terms of sensitivity and stability over wide range of relative humidity.