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 800 °C. 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 500 °C decreased the micron-sized pores and increased the proportion of the nano-sized pores, while re-sintering of the pallets at 1000 °C 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.