Wet-Chemical Fabrication of Functional Humidity Sensors on a TiO₂-Coated Glass Substrate via UV Photodeposition

This work demonstrates a completely wet-chemical procedure for the fabrication of a functional impedimetric humidity-sensing device on a titania (TiO₂) surface. Optically transparent anatase TiO₂ thin films were deposited on a glass substrate via dip-coating from a titanium tetraisopropoxide (TTIP)–acetylacetonate (AA)-based sol and surface-functionalized with a nickel oxide (NiO_x) layer by ultraviolet (UV) photodeposition. Photodeposition was employed to form the interdigitated electrode pattern on the TiO₂ surface as well through activation with a silver catalyst to promote electroless copper deposition. The relative humidity (RH) response of the pristine TiO₂- and NiO_x/TiO₂-functionalized sensors was studied by impedance (Z) measurements in the 15%–90% RH range. It was found that while NiO_x functionalization significantly dampens the RH–Z functional dependence, it improves its overall linearity and may successfully be employed for the purposeful design of titania-based sensing devices.