Hysteresis Suppression of Carbon Nanotube Thin-Film Transistor Using Laminated HfO₂/Al₂O₃ by ALD

Laminated hafnium oxide (HfO ₂ )/alumina (Al ₂ O ₃ ) fabricated by atomic layer deposition (ALD) process is employed as an encapsulation to improve the performance of carbon nanotube thin-film transistor (CNT-TFT). The outstanding hysteresis suppression ability of laminated HfO ₂ /Al ₂ O ₃ is demonstrated in the transfer characteristic of thin-film transistor (TFT) devices, with the threshold voltage variation ( $\Delta{V}_{\text {th}}$ ) of different scanning directions decreasing from ~11.06 to ~0.48 V after encapsulation, which is mainly attributed to the removal of water and oxygen molecules adsorption on the carbon nanotubes (CNTs) backchannel surface and the passivation effect to the defects at the interface between the CNTs and the gate insulator. It appears that the CNT-TFT with laminated HfO ₂ /Al ₂ O ₃ with an optimized 5 nm/5 nm structure exhibits excellent hysteresis suppression ability and performance improvement. In addition, the TFT devices with the optimal laminated HfO ₂ /Al ₂ O ₃ layers also show great reliability and gate bias stress stability.