Fabrication and Optimization of Humidity Sensor Based on Porous Nanostructure Tungsten Trioxide / Silver Nanoparticles

The aim of this research is to fabricate a moisture sensor based on porous nanostructure of pure tungsten trioxide (WO3) and doped with silver nanoparticles (SN), and to use the properties of ohmic changes, capacitance and impedance versus moisture as output. The structural characteristics of the prepared nanocomposite were examined by a scanning electron microscope and X-ray diffraction spectroscopy. The results showed that synthetic WO3 is in the form of spheres with dimensions of 3 to 7 μm, with a surface porous structure in size of 10 to 60 nm. To fabricate the sensors, first the materials were mixed and dispersed, then coated on the interdigitated electrode by sedimentation method. The investigation showed that the doped sensor with SN have a better performance in comparison with WO3 sample. Its sensitivity was obtained 4.4 and 0.68 MΩ/%RH for the relative humidity range of 20-50% and 50-90%, respectively, improved 7 and 5% compared to similar previous samples. The response and recovery time of this sensor was measured approximately 2 and 7 seconds, which is 37.5 and 41.4 times smaller than available samples, respectively. Decreasing the capacitance of the sensor to 3800 Pf by increasing the relative humidity to 90% is another finding. Significant impedance changes of the sensor versus the humidity alternations is other important result, showing that the impedance can be considered as a sensor output by compensating for errors of ohmic changes and capacitance.