Humidity Sensors Based on Doped Titania-Silica Surface Layers

The paper proposes humidity sensors on the base of Ti-Si-Ce-Zn-Cu-O surface layers, developed using a sol-gel technology and a thermal treatment at 400°C or 800°C. Titanium (IV) n-butoxide and polydimethylsiloxane have been used as titania and silica precursors. Cerium is included in the resulting system via a saturated liquid solution of diammonium hexanitrocerate in isobutanol. It provides sufficiently acidic environment for the running of the hydrolysis processes in the sol-gel system. Zinc nitrate hexahydrate and copper (II) nitrate trihydrate have been used as dopant sources of Zn and Cu. The electrical characteristics, topological features and chemical compositions of the obtained layers have been studied. The frequency characteristics of the samples have been investigated for frequencies from 20 Hz to 1 MHz. The sensitivity of the proposed sensors regarding the environment humidity is significant. The resistance variation of the sensors, sintered at 800°C, amounts to five orders of magnitude in the entire relative humidity range between 17% and 90%, registered at 20 Hz and at a temperature of 25°C.