Abnormal Bias Instabilities Induced by Lateral H<sub>2</sub>O Diffusion Into Top-Gate Insulator of a-InGaZnO Thin-Film Transistors
Jiye Li, Hao Peng, Huan Yang, Xiaoliang Zhou, Lei Lü, Shengdong Zhang
Abstract
The environmental stability of self-aligned top-gate (SATG) a-InGaZnO thin-film transistor (TFT) was studied by performing the high-temperature high-humidity (HTHH) test. Despite the maintenance of initial electrical characteristics, the stability under positive bias stress (PBS) was considerably deteriorated, including an abnormal negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\mathrm{ th}}$ </tex-math></inline-formula> shift ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol{\Delta } {V} _{\mathrm{ th}}$ </tex-math></inline-formula> ), increased off current, and degraded <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SS</i> . Moreover, the negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Delta } {V} _{\mathrm{ th}}$ </tex-math></inline-formula> was consistently enhanced with the channel length ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}$ </tex-math></inline-formula> ) decreasing. Such <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}$ </tex-math></inline-formula> dependence was clarified to originate from the lateral diffusion of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O in TG insulator during HTHH tests, and the PBS instabilities were caused by the ionization and migration of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O molecules into the a-IGZO channel, as verified by the X-ray photoelectron spectroscopy, C-V characteristics, and recovery behaviors of PBS degradation.