Highly Scaled BEOL-Compatible Thin Film Transistors With Ultrathin Atomic Layer Deposited Indium–Tin–Zinc–Oxide Channel

In this article, we have demonstrated the utilization of innovative atomic-layer-deposited (ALD) ultrathin ( $\sim$ 1.8 nm) amorphous InSnZnO ( $\alpha$ -ITZO) channel material in the development of a back-end-of-line (BEOL) compatible thin film transistor (TFT). Through the optimization of the indium/tin/zinc (In/Sn/Zn) ratio, the bottom gate (BG) TFT with In $_{\text{0}.\text{83}}$ Sn $_{\text{0}.\text{11}}$ Zn $_{\text{0}.\text{06}}$ O channel and the channel length ( $\textit{L}_{\text{ch}}$ ) of 40 nm demonstrates remarkable performances, including positive threshold voltage ( $\textit{V}_{\text{th}}$ ) of 0.38 V, excellent subthreshold swing (SS) value of 66.4 mV/dec, high field-effect mobility ( $\mu$ $_{\text{FE}}$ ) of 48 cm $^{\text{2}}$ /V-s, maximum ON-state current density ( $\textit{I}_{\text{ON}}$ ) of 686 $\mu$ A/ $\mu$ m at $\textit{V}_{\text{DS}}$ $=$ 2 V (@ $\textit{V}_{\textit{G}}$ $=$ 4 V), and extremely low drain-induced barrier lowering (DIBL) performance of 22 mV/V. Furthermore, the excellent stabilities of the $\alpha$ -ITZO TFT were shown by negative bias stress (NBS) and positive bias stress (PBS) under $\textit{V}_{\textit{G}}$ of ( $\textit{V}_{\text{th}}$ $\pm$ 3 V), and $\textit{V}_{\text{th}}$ shift ( $\Delta \textit{V}_{\text{th}}$ ) of $-$ 40 and 60 mV ( $\textit{L}_{\text{ch}}$ $=$ 700 nm) after 3600 s was exhibited. We also simulated the current gain cutoff frequency ( $\textit{f}_{\textit{T}}$ ) by technology computer-aided design (TCAD) simulation to further investigate the potential of radio frequency (RF) applications. These results establish a competitive standard for TFTs based on quaternary ultrathin ( $\textit{T}_{\text{ch}}$ $<$ 5 nm) amorphous oxide semiconductors (AOSs).