Tuning the inhomogeneous charge transport in ZnO interfaces for ultrahigh on/off ratio top-gated field-effect-transistor arrays

The interface between oxide/oxide layers shows an inhomogeneous charge transport behavior, which reveals a high conductivity owing to interface-doped. One typical example is the hetero-interface between ZnO film and other wide band gap oxides (e.g., Al₂O₃, TiO₂, and HfO₂). It is thus quite evident that the ZnO/other oxides hetero-interface contains high density electron carriers effectively screening the gate-induced electric field. Thus, an extremely weak gate modulation in ZnO film was showed, resulting in very low on/off ratio of 1.69 in top-gate field-effect-transistor (TG-FET) configuration. So, to extend the usage of ZnO TG-FET is not quite possible toward further practical application. Herein, we clarified the correlation of inhomogeneous region in oxide/oxide hetero-junction by systematically study. Our work suggests that a self-assembly of molecules (SAM) buffer layer is suitable for tuning the inhomogeneous charge transport in ZnO film, which not only reduces the interface trap density, but also effectively enhances the gate electric field modulation at the hetero-interface. We further report the robust fabrication of TG-FET arrays based on ZnO thin film, using an ultra-thin alkylphosphonic acid molecule monolayer as buffer layer. Our device demonstrates a pronounced ultrahigh on/off ratio of ≥ 10⁸, which is 8-order of magnitude higher than that of a device without buffer layer. For the highly reliable arrays, our device exhibits a high yield of over 93% with an average on/off ratio of ~10⁷ across the entire wafer scale, mobility (18.5 cm²/(V·s)), an extended bias-stressing (~ 2,000 s) and long-stability (~ 150 days) under ambient conditions.