Compositional Engineering of Hf-Doped InZnSnO Films for High-Performance and Stability Amorphous Oxide Semiconductor Thin Film Transistors

The Hf-doped indium zinc tin oxide (Hf:InZnSnO) channel for high performance and stable transparent thin film transistors (TFTs) is developed by using a simultaneous cosputtering of InZnSnO and HfO₂ targets. The effects of In and Hf composition in Hf:InZnSnO channel on the performance and stability under bias stress for the Hf:InZnSnO channel-based TFTs are investigated. Herein, the In cations enhance the electrical properties, while the Hf cations reduce the oxygen vacancies in the Hf:InZnSnO channel layer. Adjusting the atomic ratio of In of the InZnSnO target improves the performance of the Hf:InZnSnO-based TFTs, while introducing an adequate amount of HfO₂ improves the bias stabilities and hysteresis characteristics of the Hf:InZnSnO-based TFTs. The transparent TFT with optimized Hf:InZnSnO channel, with a stoichiometry of Hf_0.27In_25.96Zn_6.99Sn_6.16O_60.62, that is cosputtered at RF power of 100 W applied to InZnSnO target (In:Zn:Sn = 4:1:1 at%), and RF power of 50 W applied to HfO₂ target exhibits a field effect mobility of 11.84 cm² V⁻¹ s⁻¹ and low shift of threshold voltage of less than 2.5 V under bias stress for 3000 s. The high performance and stability of the Hf:InZnSnO channel-based TFTs demonstrate the feasibility of transparent TFTs-related next-generation display applications.