High transconductance and current density in field effect transistors using arrays of bundled semiconducting carbon nanotubes

Abstract

We examine if the bundling of semiconducting carbon nanotubes (CNTs) can increase the transconductance and on-state current density of field effect transistors (FETs) made from arrays of aligned, polymer-wrapped CNTs. Arrays with packing density ranging from 20 to 50 bundles μm−1 are created via tangential flow interfacial self-assembly, and the transconductance and saturated on-state current density of FETs with either (i) strong ionic gel gates or (ii) weak 15 nm SiO2 back gates are measured vs the degree of bundling. Both transconductance and on-state current significantly increase as median bundle height increases from 2 to 4 nm, but only when the strongly coupled ionic gel gate is used. Such devices tested at −0.6 V drain voltage achieve transconductance as high as 50 μS per bundle and 2 mS 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 still possible if the largest (95th percentile) bundles in an array are limited to ∼5 nm in size. Radio frequency devices with strong, wraparound dielectric gates may benefit from increased device performance by using moderately bundled as opposed to individualized CNTs in arrays.

Networks of Conjugated Polymer-Wrapped Single-Walled Carbon Nanotubes through Controlled Drop-Dispensing for Thin-Film Transistors

“…These results suggest that while a better distribution of the SWNTs within the drop may be obtained as temperature is increased, the observed bundling and reduced linear density leads to a drop in device performance. This drop or inconsistency in TFT performance with increased bundling has been reported for other SWNT systems. , …”

Parameters Affecting Interfacial Assembly and Alignment of Nanotubes

“…29 Future work will focus on taking advantage of subphase modification to increase nanotube alignment and uniformity while also preventing deleterious nanotube aggregation into larger bundles (>5 nm in size) that are more difficult to electrostatically gate. 29 We also investigate the effect of ethanol in the water subphase to study how decreasing the subphase surface tension affects the TaFISA alignment. Through previous work, we have determined that the ethanol stabilizer (as opposed to the amylene stabilizer) in chloroform is vital to achieve alignment in FESA films.…”

“…While individualized nanotubes are thought to be more desirable, bundled nanotubes may still be sufficient for high-performance devices as recent work demonstrated high transconductance and current densities in FETs based on arrays of bundled nanotubes. 29 Future work will focus on taking advantage of subphase modification to increase nanotube alignment and uniformity while also preventing deleterious nanotube aggregation into larger bundles (>5 nm in size) that are more difficult to electrostatically gate. 29 We also investigate the effect of ethanol in the water subphase to study how decreasing the subphase surface tension affects the TaFISA alignment.…”

“…The POM uniformity with an intermediate amount of glycerol added to the water subphase is promising; however, comparison of the SEM insets from depositions (Figure a,b,c) and AFM measurements (Figure d,e,f) shows that the addition of glycerol increases the nanotube bunching while at the same time marginally increasing the thickness of the nanotube layer, indicating multilayers or a small degree of bundling. While individualized nanotubes are thought to be more desirable, bundled nanotubes may still be sufficient for high-performance devices as recent work demonstrated high transconductance and current densities in FETs based on arrays of bundled nanotubes . Future work will focus on taking advantage of subphase modification to increase nanotube alignment and uniformity while also preventing deleterious nanotube aggregation into larger bundles (>5 nm in size) that are more difficult to electrostatically gate …”