Improving the Performance of ZnO Thin-Film Transistors with ZnON Source/Drain Contacts

Abstract

Motivation to study the ZnO channel for thin-film transistors (TFTs) is strong in light of its decent high mobility and large bandgap, enabling simultaneous coexistence of high on current and low off-state leakage. Nevertheless, the improvement in device performance for ZnO TFTs has not been fully exercised and even the field-effect mobility ( $\mu _{\text {FE}}$ ) is degraded with downscaling the channel length owing to considerable series source/drain (S/D) resistance ( ${R}_{\text {SD}}$ ). In this paper, we show that inserting a thin contact layer of ZnON between the ZnO channel and Al S/D effectively suppresses the formation of interfacial layer of AlO x and thereby reduces ${R} _{\text {SD}}$ dramatically. This is evidenced by a significant reduction in ${R} _{\text {SD}}$ from 30.1 to 14.4 $\text{k}\Omega \cdot \mu \text{m}$ measured on 0.5- $\mu \text{m}$ ZnO TFTs with a ZnON contact layer or not, leading to an improvement in $\mu _{\text {FE}}$ from 18.2 to 29.6 cm $^{2}/\text {V}\cdot \text {s}$ .