Investigation of morphological dependence on the sensing performance of porous anodic alumina based humidity sensor at low RH

Humidity sensing at low RH level (below 30%) is challenging. Since sensing is a surface activity induced phenomenon, therefore, maneuvering shape and size of surface morphology in a customized fashion is a necessity. In this report, humidity sensing characteristics of sensors with different pore morphologies were thoroughly explored. For this, three capacitive sensors with identical electrode configuration and geometry were fabricated by anodization at different anodic polarization. Sulphuric-, oxalic- and phosphoric acids were used as electrolytes to vary the pore morphology. Pores of small, medium and large dimension in nanoscale were fabricated by varying anodic polarization. Sensor response characteristics have been examined and found that both the morphology and the electrolyte composition play a decisive role in determining the capability of the sensor of its measurement level in terms of RH. The prepared sensors having various degree of sensitivity show excellent response characteristics at low RH (3%-30%) detection. Besides, the performance of the sample anodized in oxalic acid is found optimum among the three samples.