Porosity modification for the adjustment of the dynamic range of ceramic humidity sensors

The effect of the change of porosity and pore-size distribution on the sensitivity and the dynamic range of the rutile-based resistive humidity sensors is reported. Bead-type resistive humidity sensors were fabricated by the sintering of the rutile powder aggregates on the two adjacent platinum wires at 800degC. Porosity modifications were carried out in two different directions: Sol-gel impregnation of the titanium dioxide into the porous structure of the ceramic bead followed by an annealing at 500degC decreased the micron-sized pores and increased the proportion of the nano-sized pores, while re-sintering of the pallets at 1000degC eliminated the fine pores and increased the population of the micron-sized pores. Sensitivity measurements showed a shift of the useful dynamic range of the sensor towards lower relative humidity (RH) range (0-20 %) in the first group, while the second group demonstrated better performance at the higher RH range (60-100 %). It was shown that the ceramic sensors of desired RH dynamic range can be fabrication based on the pallets of predetermined pore-size distribution.