Fabrication of humidity monitoring sensor using porous silicon nitride structures for alkaline conditions

Porous silicon nitride structures were fabricated for a humidity sensor. The porous silicon structures were fabricated by the metal-assisted chemical etching process, and the conformal silicon nitride thin film was deposited by the atomic layer deposition process. The optimized porous sensor with the 10 nm-thick silicon nitride thin film had a hydrophilic surface and compared to other sensors, had an excellent humidity sensing response. Especially, it showed a superior humidity sensing response at 1 kHz with fast response and recovery times of 13.3 s and 12.4 s, respectively, were observed. Based on the electrochemical impedance spectroscopy results, the equivalent circuits and humidity sensing mechanism were discussed. The chemical stability of the silicon nitride was characterized using Tafel analysis in alkaline electrolytes. Additionally, the sensor's humidity sensing capabilities were tested under cement-embedded conditions.