First Demonstration of BEOL-Compatible Atomic-Layer-Deposited InGaZnO TFTs with 1.5 nm Channel Thickness and 60 nm Channel Length Achieving ON/OFF Ratio Exceeding 10<sup>11</sup>, SS of 68 mV/dec, Normal-off Operation and High Positive Gate Bias Stability
Jie Zhang, Zhuocheng Zhang, Zehao Lin, Ke Xu, Hongyi Dou, Bo Yang, X. Zhang, Haiyan Wang, Peide D. Ye
Abstract
In this work, we report on the first demonstration of atomic-layerdeposited (ALD) InGaZnO (IGZO) thin film transistors (TFTs) with extreme scaled channel thickness $( \mathrm{T}_{ch})$ of 1.5 nm and channel length $( \mathrm{L}_{ch})$ of 60 nm. These ALD IGZO TFTs exhibit desirable electrical performance including a high on/off ratio exceeding $10 ^{11}$, a steep subthreshold swing (SS) of 68 mV/dec, a small DIBL of 30 mV/V and a normal-off operation. By optimizing the duration of O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> annealing at $250 ^{\circ}\mathrm{C}$, the threshold voltage $( \mathrm{V}_{T})$ roll-off issue at scaled L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</inf> is resolved together with a remarkably high degree of stability to the positive gate bias stress (PBS). A trap model with its possible microscopic origin is proposed, providing a new insight into the reliability of IGZO TFTs.