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 1011, SS of 68 mV/dec, Normal-off Operation and High Positive Gate Bias Stability

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
2
annealing at $250 ^{\circ}\mathrm{C}$, the threshold voltage $( \mathrm{V}_{T})$ roll-off issue at scaled L
ch
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.