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

Abstract

In this article, the mechanism of stability in amorphous indium-gallium-zinc oxide ( a -IGZO) thin-film transistors (TFTs) with a natural length of ∼ 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 ( VTH) 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 μFE of 22.3 ±0.5 cm 2V−1s−1 , subthreshold swing (SS) of 64 ±0.5 mVdec −1 , hysteresis of 4 mV, and ΔVTH of 124 mV under harsh PBTS with E of 4 MV/cm at 80 °C for 3600 s.