Tuning the threshold voltage of a transistor is crucial for realizing robust digital circuits. For silicon transistors, the threshold voltage can be accurately controlled by doping, mainly through ion implantation. However, it remains challenging to tune the threshold voltage of single-wall nanotubes (SWNTs) thin-film transistor (TFTs).

Here, we report a facile method to controllably n-dope SWNTs using 1H-benzoimidazole and benzimidazolium derivatives processed via either solution coating or vacuum deposition, respectively. The threshold voltages of our polythiophene-sorted SWNT TFTs can be tuned accurately and continuously over a wide range. Photoelectron spectroscopy (PES) measurements confirmed that the SWNT Fermi level shifted to the conduction band edge with increasing doping concentration. Utilizing this approach, we proceeded to fabricate SWNT complementary inverters by inkjet printing of the dopants. We observed an unprecedented noise margin of 28V at VDD = 80V (70% of 1/2VDD) and a gain of 85. Additionally, robust SWNT CMOS inverter (noise margin 72% of 1/2VDD), NAND and NOR logic gates with rail-to-rail output voltage swing and sub-nanowatt power consumption were fabricated onto a highly flexible substrate for the first time.

Huiliang (Evan) Wang

Stanford University

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