Humidity sensor using porous tape cast alumina substrate

Moisture sensors based on porous alumina were designed and fabricated to detect and measure the concentration of moisture in gases. In the thin alumina disks taken, the surface and penetration effect has been considered during the process of adsorption and absorption of water molecules through pores and grain boundaries. Three different fabrication techniques, the tape casting technique, pelletization, and porous thick film, have been tried to achieve the desired moisture-sensing property of the samples. Different types of electrode structures and designs were also investigated and optimized to obtain maximum sensitivity. Electrodes were formed by screen printing the samples with thick film conductive pastes. The planar porous alumina sensor so obtained is found to be sensitive in the range of the 100-1000 ppmv level of moisture. The response time of the sensor in the ppmv range is approximately 2 min, and at higher concentrations of moisture it shows quasilinear dependency on the moisture content. (C) 2001 American Institute of Physics.