Highly Bendable Regioregular Poly(3-alkylthiophene) Sorted Semiconducting Single-Walled Carbon Nanotube Transistors and CMOS Inverters
Authors:Jeff Han, Evan Wang
Mentor:Zhenan Bao, Professor of Chemical Engineering, Stanford
Single-walled carbon nanotubes (SWNTs) are well-known for their extraordinary mechanical and electrical properties and possible applications in flexible electronics systems. The challenge remains, however, in effectively separating semiconducting (sc-) SWNTs from metallic (met-) ones to form uniform, large-area semiconducting active layers. Furthermore, selective, unipolar n-doping of intrinsically p-type SWNT transistors is essential for CMOS applications. In this work, regioregular poly(3-alkylthiophene)s (rr-P3ATs) were used to disperse sc-SWNTs for the active layer of thin-film transistors on a flexible polyimide substrate. This highly effective dispersion method yielded high-performance transistors with an on/off ratio of up to 10^6 and a mobility of up to 1.18 cm^2/Vs. n-Doping of these transistors was done by evaporating 2-(2-methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide (o-MeO-DMBI-I) onto selected device channels which yielded n-type devices with an on/off ratio of up to 10^7 and a mobility of up to 0.779 cm^2/Vs. The transistors were bent down to a 2.5 mm bending radius with no effect on device performance. The p- and n-type transistors were then used to fabricate CMOS inverters with high gains of up to 42. The effective dispersion of sc-SWNTs and the unipolar doping of selected transistors allow for the fabrication of CMOS technologies and demonstrates the viability of this platform in future flexible integrated circuits.