Semiconducting carbon nanotubes (s-CNTs) have emerged
as a promising
alternative to traditional silicon for ultrascaled field-effect transistors
(FETs), owing to their exceptional properties. Aligned s-CNTs (A-CNTs)
are particularly favored for practical applications due to their ability
to provide higher driving current and lower contact resistance compared
with individual s-CNTs or random networks. Achieving high-semiconducting-purity
A-CNTs typically involves conjugated polymer wrapping for selective
separation of s-CNTs, followed by self-assembly techniques. However,
the presence of the polymer wrapper on A-CNTs can adversely impact
electrical contact, gating efficiency, carrier transport, and device-to-device
variations, necessitating its complete removal. While various methods
have been explored for polymer removal, accurately characterizing
the extent of removal remains a challenge. Traditional techniques
such as absorption spectroscopy and X-ray photoelectron spectroscopy
(XPS) may not accurately depict the remaining polymer content on A-CNTs
due to their inherent detection limits. Consequently, the performance
of FETs based on pure polymer-wrapper-free A-CNTs is unclear. In this
study, we present an approach for preparing high-semiconducting-purity
and polymer-wrapper-free A-CNTs using poly[(9,9-dioctylfluorenyl-2,7-dinitrilomethine)-(9,9-dioctylfluorenyl-2,7-dimethine)]
(PFO-N-PFO), a degradable polymer, in conjunction with a modified
dimension-limited self-alignment process (m-DLSA). Comprehensive transmission
electron microscopy (TEM) characterizations, complemented by absorption
and XPS characterizations, provide robust evidence of the successful
near-complete removal of the polymer wrapper via a cleaning procedure
involving acidic degradation, hot solvent rinsing, and vacuum annealing.
Furthermore, top-gated FETs based on these high-semiconducting-purity
and polymer-wrapper-free A-CNTs exhibit good performance metrics,
including an on-current (I
on) of 2.2 mA/μm,
peak transconductance (g
m) of 1.1 mS/μm,
low contact resistance (R
c) of 191 Ω·μm,
and negligible hysteresis, representing a significant advancement
in the CNT-based FET technology.
