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

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.

Automated summary

By using Ar-ion etching to remove the top layer of the electrode surface before nanotube placement, the contact resistance at the nanotube-metal interface can be significantly reduced. This results in a tenfold decrease in the median ON-resistance of transistors and a more than two orders of magnitude decrease in the interquartile range of resistance values.