Study of ZnO/BST interface for thin-film transistor (TFT) applications

This work presents an investigation of ZnO/BST interface for the potential use of (Ba,Sr)TiO3 as a gate-dielectric in ZnO based thin-film transistors (TFTs) for low-voltage operation. A metal-insulator-semiconductor capacitor (MIS-C) structure, which consists of a Pt/BST/ZnO stack, was fabricated on a corning glass substrate. The capacitance-voltage (C-V) characteristic of MIS-C gives the capacitance peak in both forward and backward sweep. This peak behavior of BST is due to its paraelectric nature attributed by changing the direction of a polar molecule over the applied electric field. C-V curve of ZnO/BST MIS-C structure exhibits a counter-clockwise hysteresis of -1.33 V due to the existence of donor-like oxygen vacancies present in BST and ZnO interface. The subthreshold slope of the device was found to be 203 mV/ decade and calculated using the measurement of interface state density (Dit). ZnO/BST interface also exhibits a very low value of leakage current density (3.148 x 10(-7) Acm(-2)). Thus, the use of BST as a gate-dielectric in ZnO TFT has excellent potential, owing to its steep subthreshold slope, which implies fast switching and low off-state current.