Atomic-Layer-Deposited In–Sn–O Thin-Film Transistors With Robust Thermal Stability at 400 °C and Downscaling of Channel

Ultrathin indium tin oxide (ITO) films are investigated for back-end-of-line (BEOL) compatible thin-film transistors (TFTs) by plasma-enhanced atomic layer deposition (PEALD). By optimizing the ITO channel composition and thickness and a novel post-channel annealing (PCA) process, the resulting TFT exhibits high performance ( <tex-math notation="LaTeX">μ FE</tex-math> <tex-math notation="LaTeX">=</tex-math> 28.3 cm <tex-math notation="LaTeX">²</tex-math> /V <tex-math notation="LaTeX">·</tex-math> s, <tex-math notation="LaTeX">Vₜₕ</tex-math> <tex-math notation="LaTeX">=</tex-math> <tex-math notation="LaTeX">$-$</tex-math> 0.29 V, SS <tex-math notation="LaTeX">=</tex-math> 123 mV/dec, and <tex-math notation="LaTeX">ION/IOFF</tex-math> <tex-math notation="LaTeX">$=$</tex-math> 8.1 <tex-math notation="LaTeX">×</tex-math> 10 <tex-math notation="LaTeX">⁹)</tex-math> and especially extraordinary thermal stability. The thermal treatment at 400 <tex-math notation="LaTeX">∘</tex-math> C for 60 min in N <tex-math notation="LaTeX">₂</tex-math> only generates very small variations of <tex-math notation="LaTeX">$-$</tex-math> 0.17 V and <tex-math notation="LaTeX">$-$</tex-math> 1.4% for <tex-math notation="LaTeX">Vₜₕ</tex-math> and <tex-math notation="LaTeX">μ FE</tex-math> , respectively. Moreover, the optimized device also shows excellent positive/negative bias temperature stress (PBTS/NBTS) stabilities even at 2 MV/cm and 125 <tex-math notation="LaTeX">∘</tex-math> C. Furthermore, when the channel length is reduced to 60 nm, the outstanding electrical performance is demonstrated, such as an <tex-math notation="LaTeX">ION/IOFF</tex-math> <tex-math notation="LaTeX">~</tex-math> 10 <tex-math notation="LaTeX">¹⁰</tex-math> , an <tex-math notation="LaTeX">ION</tex-math> of 715 <tex-math notation="LaTeX">μ</tex-math> A/ <tex-math notation="LaTeX">μ</tex-math> m, and an <tex-math notation="LaTeX">RC</tex-math> of 0.542 <tex-math notation="LaTeX">Ω ·</tex-math> mm. Thus, our work provides a promising candidate for BEOL compatible transistors in monolithic 3-D integration.