Tuning the threshold voltage of carbon nanotube transistors by n-type molecular doping for robust and flexible complementary circuits

Abstract

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. However, it remains challenging to tune the threshold voltage of single-wall nanotube (SWNT) thin-film transistors. Here, we report a facile method to controllably n-dope SWNTs using 1H-benzoimidazole derivatives processed via either solution coating or vacuum deposition. The threshold voltages of our polythiophene-sorted SWNT thin-film transistors can be tuned accurately and continuously over a wide range. Photoelectron spectroscopy measurements confirmed that the SWNT Fermi level shifted to the conduction band edge with increasing doping concentration. Using this doping approach, we proceeded to fabricate SWNT complementary inverters by inkjet printing of the dopants. We observed an unprecedented noise margin of 28 V at V DD = 80 V (70% of 1/2V DD ) and a gain of 85. Additionally, robust SWNT complementary metal−oxide−semiconductor inverter (noise margin 72% of 1/2V DD ) and logic gates with rail-torail output voltage swing and subnanowatt power consumption were fabricated onto a highly flexible substrate. nanomaterials | n-doping | inkjet-printed | CMOS circuit F lexible electronics have attracted increasing attention recently due to the plethora of possible and realized applications in radio-frequency identification cards (1, 2), flexible displays (3, 4), and digital processors (5). Solution-processed single-walled carbon nanotubes (SWNTs) are a promising candidate for flexible circuits due to their high charge carrier mobility (6), excellent flexibility/stretchability (7-9), and their compatibility with lowcost, large-area manufacturing processes, such as printing (1, 10) of SWNTs. Their applications in thin-film transistors (TFTs) and integrated logic circuits (11-14) have been demonstrated. However, to achieve robust digital circuits with high immunity against the influence of electronic noise in the system, it is important to be able to control the specific value of the threshold voltage of a transistor during the fabrication process (15,16). This is because transistor threshold voltage determines the input voltage at which a circuit switches between two logic states (trip voltage of an inverter). When the trip voltage is half of the supply voltage, the circuit has the largest noise margin, which is a quantitative measure of the immunity of a logic circuit against noise and a figure of merit to characterize the robustness of the circuit (17, 18). If threshold voltage cannot be controlled during the fabrication process, the resulting circuit might not work reliably due to the electrical noise that is always present in the system. Because SWNTs have ambipolar electrical transport properties (19), accurately tuning the threshold voltage permits the construction of complementary metal−oxide−semiconductor (CMOS) circuits that use both the p-type and n-type character of SWNTs. The advantages of CMOS circuits compared with unipolar ...

All‐Carbon Thin‐Film Transistors as a Step Towards Flexible and Transparent Electronics

“…It is desirable to convert major carrier types by a doping strategy to obtain n-type transfer characteristics, and further build up CMOS configuration, which is a requirement for realistic all-carbon logic circuits, because CMOS devices have the merits of a higher noise immunity and a lower static power consumption. [226,[228][229][230] All-carbon flexible and transparent TFTs will contribute not only to next-generation display applications but also to novel gas and biological sensors, optical detectors, radio-frequency identification tags and internet-of-things applications. [219,231] These new types of electronics allow integration of sensing, display, and interactive functionalities on a single chip.…”

Encapsulated nanowires: Boosting electronic transport in carbon nanotubes

“…We demonstrate from first principles that encapsulation of 1D atomic chains within a single-walled CNT can enhance decay of "hot" phonons by providing additional channels for thermalisation. Pacification of the phonon population growth reduces electrical resistivity of metallic CNTs by 51% for an example system with encapsulated beryllium.Carbon Nanotubes (CNTs) are the most promising candidates for nanoelectronics applications due to their excellent electrical conductivity [1][2][3]. With these properties applied in integrated circuits and in the field effect transistors' gate electrodes metallic CNTs lead the minituarisation race at the nanoscale [4].…”

“…Electric field V /L is initially uniform along the CNT length L and changes according to the Poisson equation as charge flows. Scattering rates due to the electron-phonon coupling are calculated according to (1) and depend on phonon population. The latter evolves from equilibrium n qν | eq = (e ω ν q /kT − 1) −1 during electronic transport as more phonons are excited with increase of voltage bias, while only a fraction of them can be thermalised due to phonon-phonon scattering along the CNT.…”

Switching the optical and electrical properties of carbon nanotube hybrid films using a photoresponsive dispersant as a dopant

“…H 2 SO 4 and HNO 3 ). [31][32][33] In our case, the absorption spectrum of the SWCNT/AB lm indicates the bleached S 11 bands compared with that of the SWCNT/SDOC lm and the SWCNT/AB lm with UV irradiation. Collectively, these results showed that the as-prepared SWCNT lm was doped by AB, and the appearance of the S 11 bands following UV irradiation should correspond the de-doping of photoisomerised AB.…”