Tunable hafnium-doped InZnO thin film transistors via plasma-enhanced atomic layer deposition

Abstract

Hafnium-doped InZnO (HIZO) thin film transistors (TFTs) were successfully fabricated via plasma-enhanced atomic layer deposition (PEALD) at low temperature (180 °C) for the first time, omitting the annealing process. Concretely, we adjusted the device performance by modulating the doping concentration of hafnium (Hf) cations and the oxygen vacancy content. The optimal 6.25 % doping content was determined. Based on this optimization, the HIZO TFTs exhibited an excellent field-effect mobility (μ_FE) of 21.7 cm²/V·s, a low threshold voltage (V_th) of ∼0.1 V, a minimum subthreshold swing (SS) of 69 mV/decade and a fantastic I_on/I_off of exceeding 10⁸ utilizing the hafnium oxide (HfO₂) dielectric, which was one of the state-of-the-art performances among HIZO TFTs reported to date. Meanwhile, an excellent bias stability under both positive and negative bias stress was achieved. The favorable performance can be attributed to the effective suppression of overabundant oxygen vacancies and the passivation of defects at the channel–dielectric interface by Hf doping. The Hall effect measurement and X-ray photoelectron spectroscopy (XPS) further corroborate the ability to inhibit carrier concentration by Hf addition. This study presents a novel strategy for achieving excellent HIZO TFTs, holding promise for the next-generation high-performance display domain.