Degradation Due to Photo-Induced Electron in Top-Gate In-Ga-Zn-O Thin Film Transistors With n<sup>−</sup> Region Under Negative Bias Stress and Light Irradiation
Yujiro Takeda, Takanori Takahashi, Ryoko Miyanaga, Juan Paolo Bermundo, Yukiharu Uraoka
Abstract
We investigated the positive threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}{)}$ </tex-math></inline-formula> shift with hump and on-current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {on}}{)}$ </tex-math></inline-formula> reduction in top-gate In-Ga-Zn-O (IGZO) thin film transistors (TFTs) after negative gate bias of −20 V at 60°C and light irradiation stress (NBTIS). This degradation can be classified into three types of mechanism. 1. The hump at low gate voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {g}}{)}$ </tex-math></inline-formula> is a sub-transistor effect caused by hole trapping at the IGZO/top gate insulator (TGI) interface. 2. The positive shift of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> is caused by the trapped photo-induced electrons at the IGZO/bottom gate insulator (BGI) interface. 3. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {on}}$ </tex-math></inline-formula> reduction occurred due to trapped photo-induced electrons at interface between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{n}^{-}$ </tex-math></inline-formula> region of IGZO/BGI interface. The electric field induced by trapped electron promotes depletion of the channel region at the IGZO/BGI and IGZO/TGI interface and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{n}^{-}$ </tex-math></inline-formula> region of IGZO/BGI interface, which corresponds to a drop in effective gate and drain voltage, respectively. Thus, the positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> shift and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {on}}$ </tex-math></inline-formula> reduction occurred due to trapping of photo-induced electron under NBTIS. Based on our proposed mechanism, this degradation was suppressed by the dual-gate structure.