Enhanced electrical stability and reliability of amorphous IGZO/HfO2 thin film transistors with CF4 plasma treatment

Abstract

This study investigates the enhancement of stability in a-IGZO/HfO2 thin-film transistors (TFTs) through CF4 plasma treatment at the interface between the two thin films. The presence of various point defects in HfO2 thin films contributes to reliability challenges, including alterations in threshold voltage (Vth) when subjected to positive bias stress (PBS) or positive bias temperature stress (PBTS). Furthermore, these defects play a significant role in inducing hysteresis when forward and reverse biases are applied. In particular, the presence of oxygen vacancies (Vo) and positively charged defects leads to a negative shift in the Vth during PBTS. The implementation of plasma treatment at the interface effectively diminishes the concentration of Vo and hydrogen impurities on the surface of HfO2. This reduction leads to a decrease in the number of trapped point defects at the a-IGZO/HfO2 interface, which results in a lower threshold voltage shift (ΔVth). As a result, the a-IGZO TFT demonstrated superior electrical characteristics, characterized by a mobility of 38.90 cm2/V·s, a subthreshold swing of 70 mV/decade, an approximate hysteresis of 10 mV, and ΔVth of approximately 199 mV following PBTS at a temperature of 80 °C for a duration of 3,600 s, under an applied electric field of 2 MV/cm.