Humidity sensors based on silica nanoparticle aerogel thin films

Humidity sensors were fabricated with thin films of silica nanoparticles aerogel on gold-patterned alumina substrates by sol–gel colloid spin coating and supercritical drying. The aerogel silica possesses average pore size of 20.5 nm, particle size around 30 nm, film thickness within 142 nm, and specific surface area of 866 m2/g. Both impedance and capacitance responses of the mesoporous film sensor were sensitive to moisture and operation temperature at 40% RH and higher, and with a hysteresis within 3.3% RH. Electrical resistance markedly decreased with humidity at low frequency. Porosity, surface hydroxyls, and film uniformity of silica were directly related to the sensors performance. The operation stability and reproducibility over time make the aerogel films potentially viable for use in ceramics integrated humidity sensors.