Reliability tests and improvements for Sc-contacted n-type carbon nanotube transistors

Scandium (Sc) contacted n-type carbon nanotube (CNT) field-effected transistors (FETs) with back and top-gate structure have been fabricated, and their stability in air were investigated. It was shown that oxygen and water molecules may affect both the nanotube channel and Sc/nanotube contacts, leading to deteriorated contact quality and device performance. These negative effects associated with the instability of n-type carbon nanotube FETs can be eliminated through passivating the CNT devices by a thin layer of atomic-layer-deposition grown Al₂O₃ insulator. After passivation, the n-type carbon nanotube FETs are shown to exhibit excellent atmosphere stability even after being tested and exposed to air for over 146 days, and then much smoother output characteristics and reduced gate voltage hysteresis from 1 to 0.1 V were demonstrated when compared with devices without passivation. Lasting power-on tests were also performed on the passivated CNT FETs under large gate stress and high drain current in air for at least 10 h, revealing null device degradation and sometimes even improved performance. These results promise that passivated CNT devices are reliable in air and may be used in practical applications.