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 ( <tex-math notation="LaTeX">~</tex-math> 1.8 nm) amorphous InSnZnO ( <tex-math notation="LaTeX">α</tex-math> -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 <tex-math notation="LaTeX">0.83</tex-math> Sn <tex-math notation="LaTeX">0.11</tex-math> Zn <tex-math notation="LaTeX">0.06</tex-math> O channel and the channel length ( <tex-math notation="LaTeX">Lch</tex-math> ) of 40 nm demonstrates remarkable performances, including positive threshold voltage ( <tex-math notation="LaTeX">Vₜₕ</tex-math> ) of 0.38 V, excellent subthreshold swing (SS) value of 66.4 mV/dec, high field-effect mobility ( <tex-math notation="LaTeX">μ</tex-math> <tex-math notation="LaTeX">FE</tex-math> ) of 48 cm <tex-math notation="LaTeX">²</tex-math> /V-s, maximum ON-state current density ( <tex-math notation="LaTeX">ION</tex-math> ) of 686 <tex-math notation="LaTeX">μ</tex-math> A/ <tex-math notation="LaTeX">μ</tex-math> m at <tex-math notation="LaTeX">VDS</tex-math> <tex-math notation="LaTeX">$=$</tex-math> 2 V (@ <tex-math notation="LaTeX">VG</tex-math> <tex-math notation="LaTeX">$=$</tex-math> 4 V), and extremely low drain-induced barrier lowering (DIBL) performance of 22 mV/V. Furthermore, the excellent stabilities of the <tex-math notation="LaTeX">α</tex-math> -ITZO TFT were shown by negative bias stress (NBS) and positive bias stress (PBS) under <tex-math notation="LaTeX">VG</tex-math> of ( <tex-math notation="LaTeX">Vₜₕ</tex-math> <tex-math notation="LaTeX">±</tex-math> 3 V), and <tex-math notation="LaTeX">Vₜₕ</tex-math> shift ( <tex-math notation="LaTeX">Δ Vₜₕ</tex-math> ) of <tex-math notation="LaTeX">$-$</tex-math> 40 and 60 mV ( <tex-math notation="LaTeX">Lch</tex-math> <tex-math notation="LaTeX">$=$</tex-math> 700 nm) after 3600 s was exhibited. We also simulated the current gain cutoff frequency ( <tex-math notation="LaTeX">fT</tex-math> ) 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 ( <tex-math notation="LaTeX">Tch</tex-math> <tex-math notation="LaTeX">$<$</tex-math> 5 nm) amorphous oxide semiconductors (AOSs).