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 (~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 In0.83Sn0.11Zn0.06O channel and the channel length (
${L}_{\text {ch}}$
) of 40 nm demonstrates remarkable performances, including positive threshold voltage (
${V}_{\text {th}}$
) of 0.38 V, excellent subthreshold swing (SS) value of 66.4 mV/dec, high field-effect mobility (
$\mu _{\text {FE}}$
) of 48 cm2/V-s, maximum ON-state current density (
${I}_{\text {ON}}$
) of
$686~\mu \text{A}/\mu \text{m}$
at
${V}_{\text {DS}}$
= 2 V (@
${V}_{G}$
= 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
${V}_{G}$
of (
${V}_{\text {th}}~\pm $
3 V), and
${V}_{\text {th}}$
shift (
$\Delta {V}_{\text {th}}$
) of −40 and 60 mV (
${L}_{\text {ch}}$
= 700 nm) after 3600 s was exhibited. We also simulated the current gain cutoff frequency (
${f}_{T}$
) 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 (
${T}_{\text {ch}} < 5$
nm) amorphous oxide semiconductors (AOSs).