Humidity sensitive properties of amorphous (K,Na)NbO3 lead free thin films

In this study, amorphous (K,Na)NbO3 (KNN) lead free thin films were deposited on (100) silicon substrate via RF magnetron sputtering, and the humidity sensitive properties of these films have been firstly studied. The humidity sensors based on these KNN films show a giant capacitive response of 95% at 25 Hz in the RH range 33–95% and a great linear relationship between capacitance and relative humidity (RH). The humidity sensing mechanism of amorphous KNN films was well described, and its high performance was correlated to a large amount of intrinsic hydrophilic groups K–O and Na–O bonds as well as the rough structure on the amorphous film surfaces, thereby, accelerating the adsorption and desorption of multi-physisorbed water molecules. This conclusion was further confirmed by a comparison studies between KNN amorphous film and bulk ceramics (response time: 1.0 min vs. >10 min; recovery time: 2.0 min vs. 7 min).