Arrays of Bundled Semiconducting Carbon Nanotubes for High Transconductance Field Effect Transistors

Forming aligned arrays from bundled (rather than individualized) semiconducting carbon nanotubes can beneficially increase the density of nanotubes in the channel of field effect transistors (FETs). Here, we prepare aligned arrays of bundles at a density of 20 – 50 bundles μm-1 via tangential flow interfacial self-assembly and show that bundles can increase the transconductance of FETs when a strong gate is used. When encapsulated with an ion gel gate, the transconductance and saturated on-current increases as the diameter of the bundles increases. Devices tested at -0.6 V drain voltage using an ion gel gate achieve transconductance as high as 50 μS per bundle and 2000 μS μm-1 and on-state current as high as 1.7 mA μm-1. At low drain voltages the off-current also increases with bundling, but on/off ratios of ~105 are possible if the bundle size is limited to ~ 5 nm. Radio frequency devices with very strong gates may benefit from the increased device performance by using moderately bundled semiconducting carbon nanotube arrays. Figure Caption: Panel (a) has transfer curves from 4 devices each with ~42 CNTs-bundles μm-1 but with different median bundle heights. Devices with larger bundles have higher transconductance and saturated on-currents. Panel (b) shows the transconductance per bundle vs the median bundle height and shows the positive correlation between bundle size (height) and transconductance per bundle. Panel (c) is a rendering of a large bundle formed from polymer wrapped CNTs. Figure 1