Positive Bias Stress Instability of InGaZnO TFTs With Self-Aligned Top-Gate Structure in the Threshold-Voltage Compensated Pixel (2019)

The instability induced under positive gate-bias stress (PBS) in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) with self-aligned top-gate coplanar structure is investigated under the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">threshold-voltage</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$({V}_{T})$ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">compensated pixel scheme</i> in the backplane of organic light-emitting diode displays and compared with that under a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">constant-PBS scheme</i> . Based on the investigation, which combines the extraction of density of states, the decomposition of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </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">$\Delta {V}_{T}$ </tex-math></inline-formula> ), and technology computer-aided design, the unreleased electric field across the gate insulator (GI) and the maintained electron concentration are observed under the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> -compensated PBS condition. Indeed, the main difference between the two schemes originates from increasingly activated electron trapping within the GI deep-level traps and from the excessive oxygen-related peroxide bond-breaking in the a-IGZO-active film, i.e., O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2−</sup> + <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 {e}^{-} \to$ </tex-math></inline-formula> O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2−</sup> + O <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2−</sup> . Although the latter is quantitatively much smaller than the former, the two mechanisms are closely related to each other and should be jointly optimized. This is because a large amount of oxygen interstitials can generate a high density of GI electron traps. Since the GI deep-level trapping results in noticeable <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{T}$ </tex-math></inline-formula> with an increase in PBS time, our results suggest that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{T}$ </tex-math></inline-formula> should be seriously underestimated with respect to either the estimation of pixel lifetime or the assessment of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> -compensated pixel-circuit schemes, if the reliability/acceleration test relies only on the constant-PBS-based single-TFT device test.