Boosting Carrier Mobility in Zinc Oxynitride Thin-Film Transistors via Tantalum Oxide Encapsulation

Novel TaOx encapsulation was presented to enhance the field-effect mobility of ZnON thin-film transistors (TFTs), consisting of a metallic Ta film deposited onto the ZnON surface followed by a modest annealing process. The resulting TaOx/ZnON film stack exhibited a more uniform distribution of nanoscale ZnON crystallites with increased stoichiometric anion lattices compared to the control ZnON film. The control ZnON TFTs exhibited a reasonable mobilty, subthreshold gate swing (SS), and ION/OFF ratio of 37.8 cm2/Vs, 0.29 V/decade, and 2.9 × 108, respectively. A significantly enhanced mobility of 89.0 cm2/Vs was achieved for ZnON TFTs with a TaOx encapsulation layer, whereas SS of 0.34 V/decade and ION/OFF ratio of 8.6 × 108 were comparable to those of the control device. This improvement could be explained by scavenging and passivation effects of the TaOx film on the ZnON channel layer. Density-of-state (DOS)-based modeling and simulation was performed to obtain greater insight with regard to increasing th...