Electrical conduction in (Ba, Sr)TiO3 thin film MIS capacitor under humid conditions

Barium strontium titanate (BST) thin films are made on n-type Si substrate by the sol–gel technique to study electrical conduction in a metal–insulator–semiconductor (MIS) device under humid conditions. These films are porous and adsorb the water vapour when exposed to a humid environment. Due to adsorption of the water vapor, a large shift of ∼1 volt in flat band voltage from C–V measurements is observed. An attempt has been made to understand the current conduction mechanism in these films under different humidity conditions. Impedance measurements have been made at various frequencies and at different humidity levels to distinguish individual contributions to electrical conduction, arising from different sources like bulk and grain boundaries, inter granular contact regions and electrode–sample interface regions on the basis of non-Debye theory. We have proposed a physical model and its equivalent circuit to explain the skewed semicircles in the Cole–Cole plot of the experimentally acquired data.