High bias stability of Hf-doping-modulated indium oxide thin-film transistors

Device stability is one of the key parameters for transistor applications. To improve the stability of Indium oxide (In₂O₃) after a long-time gate bias, a synthetic solution of hafnium chloride (HfCl₄) and indium nitrate (In(NO₃)₃∙xH₂O) reagents were used to obtain 0% to 5-at.% Hf doped In₂O₃ thin-film transistors. With the increase of Hf doping concentration, oxygen vacancies and residual hydroxyl groups continue to decrease, suppressing the carrier concentration and influencing the trap state density of In₂O₃. The sub-threshold slope (SS) 0.78 V·dec⁻¹ for the undoped In₂O₃ transistor in this work is a typical value. When the dopant dose is up to 5-at.%, SS decreases to 0.32 V·dec⁻¹. According to the proportional relationship between SS and the density of trap states, it shows that the density of trap states in the dielectric layer and the semiconductor/dielectric interface SS is greatly reduced after 5-at.% Hf doping. The probability of the charge being trapped is dropped as well. At the same time, under the doping of Hf, the transistor exhibits a very small threshold voltage shift. Especially at the dopant dose of 5-at.%, the transfer characteristic curve hardly shifts. This work demonstrates an In₂O₃ transistor with high bias stability by doping method.