Analysis of a-InGaZnO TFT Threshold Voltage Instability and Mobility Boosting by Current Stress at a Cryogenic Temperature
Sangwon Lee, Jingyu Park, Ga Won Yang, Changwook Kim, Sung‐Jin Choi, Dong Myong Kim, Jong‐Ho Bae, Dae Hwan Kim
Abstract
Device characteristics of amorphous InGaZnO thin film transistors (a-IGZO TFTs) at a cryogenic temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}$ </tex-math></inline-formula> ) are analyzed including device instability after applying current stress. Threshold voltage instability ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{\mathrm{T}}$ </tex-math></inline-formula> ) mechanisms are analyzed before and after applying stress in the two TFTs with different oxygen flow rates in the formation of a-IGZO active layers (O-poor and O-rich TFTs). <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{\mathrm{T}}$ </tex-math></inline-formula> of the a-IGZO TFTs at 77K are reduced less than 50% of that at 300K, because charge trapping into the gate insulator stack and the donor creation in the active layer are T- dependent processes. After applying stress at 77K, the O-poor TFT has better stability than the O-rich TFT, but the O-rich TFT exhibits a mobility boosting ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 1.7$ </tex-math></inline-formula> ) related to donor creation, which can increase the operating speed and reduce the operating voltage at a cryogenic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}$ </tex-math></inline-formula> operation.