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.