In this work, we reported aggressively scaled amorphous InZnOx ($\alpha$-IZO) thin film transistor (TFT) in channel length (Lch=8 nm) and thickness (2 nm) as a promising candidate for monolithic three-dimensional (M3D) integrations at back-end-of-line (BEOL). The bottom gate TFT with ultra-short Lch of 8 nm exhibited excellent sub-threshold swings (SS) value of 69 mV/dec, high filed-effect mobility ($\mu_{F}E$) of $41 cm^{2}/V-s$ and on-current density (ION) up to $575 \mu A\ \mu m (V_{DS} = 1V, V_{G}|= 2V)$ with outstanding maximum transconductance (Gm) value of $521 \mu S \mu m (V_{D}S = 1 V)$. In particular, the maximum Gm reaches 802 $\mu S \mu m$ at $V_{DS}= 2V$ and very low drain induce barrier lowering (DIBL) performance of 27.8 mV/V represent the best Gm and DIBL values reported for ternary amorphous oxide-semiconductor based TFTs. Furthermore, the highly stable device characteristics of the TFT was demonstrated with positive gate bias stress (PBS), the threshold voltage shift $\left(\Delta \mathrm{V}_{t h}\right)$ of 26.5 mV (Lch=50 nm) after 3000 s stress with VG-Vth of 3 V was observed