Mechanism of External Stress Instability in Plasma-Enhanced ALD-Derived HfO2/IGZO Thin-Film Transistors

In this article, the mechanism of stability in amorphous indium-gallium-zinc oxide ( ${a}$ -IGZO) thin-film transistors (TFTs) with a natural length of $\sim $ 8 nm was investigated from the perspective of hafnium oxide (HfO $_{{2}}{)}$ gate dielectric point defects. The point defects in HfO2 responded to external stresses such as electric field ( ${E}{)}$ and temperature. In particular, oxygen vacancies and the positively charged defects caused an abnormal negative shift in threshold voltage ( ${V}_{\text {TH}}{)}$ under positive gate bias temperature stress (PBTS). Therefore, reducing the positively charged defects was important to eliminate the abnormal behavior. Inserting a 0.7-nm-thick ultrathin SiO2 interlayer between ${a}$ -IGZO and optimized HfO2 further improved device performance including stability. Consequently, the resultant ${a}$ -IGZO TFT exhibited promising device performance with $\mu _{\text {FE}}$ of 22.3 ±0.5 cm $^{{2}}\text{V}^{-{1}}\text{s}^{-{1}}$ , subthreshold swing (SS) of 64 ±0.5 mVdec $^{-{1}}$ , hysteresis of 4 mV, and $\Delta {V}_{\text {TH}}$ of 124 mV under harsh PBTS with ${E}$ of 4 MV/cm at 80 °C for 3600 s.