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Competitive impact of nanotube assembly and contact electrodes on the performance of CNT-based FETs

: Toader, M.; Hermann, S.; Scharfenberg, L.; Hartmann, M.; Mertig, M.; Schulz, S.E.; Gessner, T.


Journal of physical chemistry. C, Nanomaterials and interfaces 120 (2016), Nr.18, S.10020-10026
ISSN: 1932-7447
ISSN: 1932-7455
Deutsche Forschungsgemeinschaft DFG
Fraunhofer ENAS ()

We report the fabrication and characterization of highly dense field-effect-transistor (FET) arrays based on single-walled carbon nanotubes (SWCNTs). The nanotubes were sorted according to the electronic type by using density gradient ultracentrifugation (DGU). By employing dielectrophoresis (DEP), SWCNTs with enriched semiconducting (sc) content were systematically integrated as active elements into FETs. The performance of air-operating FETs was addressed via an extended statistic study involving both electrical and structural analyses. The competitive impact of nanotube purity and assembly as well as the metal electrode composition and a thermal treatment on the final device performance was shown. Regardless of the used sc-content, the device-to-device consistency was improved via employing annealing up to 250 degrees C for 1 h in a vacuum. The observed clockwise hysteresis, known so far only in connection with CNT-FETs built on ferroelectric substrates as well as electrolyte gated CNT-FETs, was found to reverse upon annealing. Moreover, a simple approach in producing air-stable ambipolar transistors is pointed out only via change of the adhesion layer for the Pd electrodes. The annealing study, repeated on such systems, supports the previous results and provides complementary information via a reliable monitoring of the off-state. Indications for a doping-like effect, which partially compromises the device performance in terms of threshold voltage shifts and increased off-state currents, are revealed and discussed.