Competitive Impact of Nanotube Assembly and Contact Electrodes on the Performance of CNT-based FETs

Abstract

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 °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.

Polymer-based doping control for performance enhancement of wet-processed short-channel CNTFETs

“…Afterwards, the hysteresis was clockwise. The very origin of this phenomenon is currently discussed in the literature [25,58]. However, by properly adjusting the polymerization time, the overall hysteresis can be minimized.…”

Device design and optimization of CNTFETs for high-frequency applications

“…3a, the CNT is deposited on the high-oxide grown on top of the buried gate and is then covered by a low-oxide. This corresponds to structures fabricated in [12][13][14][15][16], but the high-oxide coverage may be suboptimal, since the gate control weakens at the top of the CNT due to the lower . Thus, for comparison, the case of full high-oxide coverage around the CNT as shown in Fig.…”

Advanced Characterization Methods for Electrical and Sensoric Components and Devices at the Micro and Nano Scales

“…As one of the many applications, we can take a closer look at CNT devices. Special cases of such are interconnects formed by vertically aligned CNTs grown by means of chemical vapor deposition (CVD), mechanically bendable conductive lines made from conductive CNTs, and horizontally aligned conductive tracks using multi‐walled CNTs (MWCNTs) as well as CNTFETs using semiconducting SWCNTs . For the first case of CNT vias, local electrical probing allowed a resistivity mapping of grown CNTs or mapping down to the individual CNT .…”

“…For the second case of assemblies of MWCNTs, conductivity measurements using CS‐AFM allow insight into the role of the local morphology represented by the preferential orientation on the nanoscale of the inkjet‐printed lines on the microscopic conductivity . For the third case of CNTFETs, the initial degree of positioning, CNT assembly and alignment, contact formation as well as the doping state of the channel‐building nanomaterial turned out to be important parameters. Particular challenges of hyperlocal electrical characterization are the variations of the environmental charge distribution both locally as well as temporally.…”