Understanding and improving carbon nanotube-electrode contact in bottom-contacted nanotube gas sensors

Abstract

• Carbon nanotube-metal contact is improved by electrode surface etching with Ar-ion. • Self-heating operation of suspended carbon nanotube gas sensors is facilitated. • Surface analysis identifies main causes of poor nanotube-metal contact. Suspended carbon nanotube field-effect transistors fabricated with a dry transfer technique demonstrate strong promise as ultra-low-power, hysteresis-free gas sensors. However, the difficulty of establishing a good electrical contact between a nanotube and the electrode surface often limits the yield of low-resistance devices that can operate as low-power gas sensors. In this work, the contact resistance at the nanotube-metal interface and the distribution thereof are reduced significantly by removing the top layer of electrode surface with Ar-ion etching directly before nanotube placement. Combined with post-transfer annealing, this pre-transfer electrode surface cleaning reduces the median ON-resistance of transistors by an order of magnitude--from 1.56 MOhm to 143 kOhm--and the interquartile range by more than two orders of magnitude--from 9.38 MOhm to 59 kOhm. The ability to consistently improve nanotube-metal contact demonstrated in this work is a significant advance in the fabrication of ultraclean nanotube transistors and carbon nanotube gas sensors.