CNT Diameter Research Articles

Mg‐ZnO/CNT Nanocomposite as Electrode Materials with Enhanced Electrochemical Performance for Supercapacitor Applications

AbstractThe present research work reported the study of nanocomposites of undoped and Mg‐doped ZnO with CNT as electrode materials for supercapacitor application. The undoped ZnO/CNT and Mg‐doped ZnO/CNT nanocomposites (i.e., 10 % Mg‐doped and 20 % Mg‐doped) were synthesized using a cost‐effective blending‐assisted hydrothermal method. The morphological (FESEM & TEM) studies revealed that the diameter of CNT was ~7 nm and the ZnO nanoparticles were spherical in shape with an average particle size of ~5 nm. In addition, it was also found that 10 % Mg‐ZnO and 20 % Mg‐ZnO had a sheet‐like structure. XRD and FTIR studies further confirmed the successful doping of Mg in ZnO and CNT nanocomposites. BET analysis showed that the value of specific capacitance increased with the increase in surface area. Further, the electrochemical performance of these nanocomposites revealed that the higher doping percentage, 20 % Mg‐ZnO/CNT nanocomposite achieved the highest specific capacitance value i.e., 458.5 F/g at 0.1 A/g current density in 3M H2SO4 electrolytic solution, having a retention of 99.8 % after 12,00 long cycles. In addition, the charge storage mechanism revealed that the as‐synthesized nanocomposites showed both the diffusion‐controlled and capacitive‐controlled behaviors. Thus, a higher value of specific capacitance with excellent cyclic stability indicated the higher efficiency of Mg‐doped ZnO/CNT nanocomposite for future supercapacitor applications.

Boosting CO2 Hydrogenation to Methanol over Monolayer MoS2 Nanotubes by Creating More Strained Basal Planes.

The controlled creation, selective exposure, and activation of more basal planes while simultaneously minimizing the generation and exposure of edge sites are crucial for accelerating methanol synthesis from CO2 hydrogenation over MoS2 catalysts but remain a bottleneck. Here, we report a facile method to fabricate heteronanotube catalysts with single-layer MoS2 coaxially encapsulating the carbon nanotubes (CNTs@MoS2) through host-guest chemistry. Inheriting the long tubular structure of CNTs, the grown MoS2 nanotubes exhibit significantly more basal planes than bulk MoS2 crystals. More importantly, the tubular curvature not only promotes strain and sulfur vacancy (Sv) generation but also preferentially exposes more in-plane Sv while limiting edge Sv exposure, which is conducive to methanol synthesis. Both the strain and layer number of MoS2 can be easily and finely adjusted by altering CNT diameter and quantity of precursors. Remarkably, CNTs@MoS2 with monolayer MoS2 and maximum strain displayed methanol selectivity of 78.1% and methanol space time yield of 1.6 g gMoS2-1 h-1 at 260 °C and GHSV of 24000 mL gcat.-1 h-1, representing the best results to date among Mo-based catalysts. This study provides prospects for novel catalyst design by synthesizing coaxial tubular heterostructure to create additional catalytic sites and ultimately enhance conversion and selectivity.

Design of carbon allotrope FET-based folded cascode operational transconductance amplifiers (FC-OTA)

ABSTRACT Throughout this study, a high-gain, low-energy folded cascode operational transconductance amplifier (FC-OTA) was modelled utilising HSPICE software. The FC-OTA designs included implementations availing CNFETs, GNRFETs, and mixed involving a combination of CNFETs with CMOS. Comparison with traditional CMOS-based FC-OTAs revealed that CNFET-based FC-OTAs exhibited considerable enhancements, displaying significant escalation in DC amplification, output resistance, average power dissipation, and CMRR. The phase margin in CNT-based FC-OTAs indicated stability. Moreover, CNT-based devices showed substantial rise in direct current amplification over GNRFET-FC-OTAs. The study further explored the operational effectiveness of proposed FC-OTAs by varying parameters such as CNT diameter, CNT pitch, and the number of CNTs, identifying optimal values that significantly enhance the FC-OTA’s performance. Comprehensive parametric and Monte Carlo analyses demonstrated OTA’s resilience to changes in supply voltage, temperature, capacitance, and mismatches. In summary, the folded cascode approach was found to enhance gain and reduce average power in CNFET-based FC-OTAs in comparison to other structural configurations.

Phonon Thermal Transport at Interfaces of a Graphene/Vertically Aligned Carbon Nanotubes/Hexagonal Boron Nitride Sandwiched Heterostructure

Molecular dynamics simulation is used to calculate the interfacial thermal resistance of a graphene/carbon nanotubes/hexagonal boron nitride (Gr/CNTs/hBN) sandwiched heterostructure, in which vertically aligned carbon nanotube (VACNT) arrays are covalently bonded to graphene and hexagonal boron nitride layers. We find that the interfacial thermal resistance (ITR) of the Gr/VACNT/hBN sandwiched heterostructure is one to two orders of magnitude smaller than the ITR of a Gr/hBN van der Waals heterostructure with the same plane size. It is observed that covalent bonding effectively enhances the phonon coupling between Gr and hBN layers, resulting in an increase in the overlap factor of phonon density of states between Gr and hBN, thus reducing the ITR of Gr and hBN. In addition, the chirality, size (diameter and length), and packing density of sandwich-layer VACNTs have an important influence on the ITR of the heterostructure. Under the same CNT diameter and length, the ITR of the sandwiched heterostructure with armchair-shaped VACNTs is higher than that of the sandwiched heterostructure with zigzag-shaped VACNTs due to the different chemical bonding of chiral CNTs with Gr and hBN. When the armchair-shaped CNT diameter increases or the length decreases, the ITR of the sandwiched heterostructure tends to decrease. Moreover, the increase in the VACNT packing density also leads to a continuous decrease in the ITR of the sandwiched heterostructure, attributed to the extremely high intrinsic thermal conductivity of CNTs and the increase of out-of-plane heat transfer channels. This work may be helpful for understanding the mechanism for ITR in multilayer vertical heterostructures, and provides theoretical guidance for a new strategy to regulate the interlayer thermal resistance of heterostructures by optimizing the design of sandwich layer thermal interface materials.

An Atomistic Study of the Tensile Deformation of Carbon Nanotube-Polymethylmethacrylate Composites.

There has been growing interest in polymer/carbon nanotube (CNT) composites due to an exceptional enhancement in mechanical, structural, thermal, and electronic properties resulting from a small percentage of CNTs. However, the performance of these composites is influenced by the type of polymer used. PMMA is a polymer of particular interest among many other polymers because of its biomaterial applications due to its biocompatibility, non-toxicity, and non-biodegradability. In this research, we utilized a reactive force field to conduct molecular dynamics simulations to investigate changes in the mechanical properties of single-walled carbon nanotube (SWCNT)-reinforced Poly (methyl methacrylate) (PMMA) matrix composites. To explore the potential of SWCNT-reinforced PMMA composites in these applications, we conducted simulations with varying CNT diameters (0.542-1.08 nm), CNT volume fractions (8.1-16.5%), and temperatures (100 K-700 K). We also analyzed the dependence of Young's modulus and interaction energy with different CNT diameters, along with changes in fracture toughness with varying temperatures. Our findings suggest that incorporating a small amount of SWCNT into the PMMA polymer matrix could significantly enhance the mechanical properties of the resulting composite. It is also found that the double-walled carbon nanotube has roughly twice the tensile strength of SWCNT, while maintaining the same simulation cell dimensions.

Design of CNTFET-based Ternary Ring and Up–Down Counter Cells

In recent times, the multi-valued logic (MVL) design has been widely explored in the designing of digital computing circuits as the goals of enhanced processing capability with reduced interconnect complexity and small chip area are achieved. Hence, this work describes the design methodology of ternary logic-based asynchronous and synchronous up-counter, down-counter, and ring-counter designs using D-flip-flops in carbon nanotube technology. Carbon nanotube-field-effect transistors (CNTFETs)’ unique feature of altering the device threshold voltage by making variations in CNT diameter is exploited for the realization of multiple voltages in ternary logic design. Here the principle of the master-slave scheme is adopted for the designing of Dual shift-single shift and Single shift-dual shift-D-flip-flop circuits using the cyclic property of shifting operators. These flip-flop designs are further extended to construct multiple-digit counter structures which are suitable for realizing the logic functionality of up-counter, down-counter, and ring-counter designs. To exploit ternary logic increased computation capability benefit, a mode control up/down counter circuit is designed in which a single module is generating up and down-counting sequence based on applied mode input. To investigate the performance of the proposed designs, the simulations are performed using the Synopsys HSPICE simulator considering the 32 nm Stanford CNTFET model. According to the simulation results, a maximum energy consumption reduction up to 55% is obtained compared to the counterpart. Hence, the increased computational capability of three-valued logic is exploited in the presented work to achieve energy enhancements in designing ternary sequential circuits.

A Novel Carbon Nanotube Field Effect Transistors Based Triple Cascode Operational Transconductance Amplifier: An Optimum Design

This paper discusses a triple-cascode operational transconductance amplifier (TCOTA) circuit’s design and modeling. These proposed TCOTAs are constructed using 45 nm Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) and Carbon Nanotube Field Effect Transistors (CNTFETs). At the 45 nm technology node, three distinct varieties of CNT-based TCOTAs have been designed and contrasted with conventional CMOS-based TCOTAs. The performance of the CNT-based TCOTAs, particularly a pure CNT-TCOTA, has significantly improved, according to the assessment of the fundamental aspects of all the devices. The DC gain has been enhanced by 73% when contrasting the pure CNT-TCOTA to the conventional CMOS-TCOTA, the CMRR has improved by 28%, and the power consumption has been reduced by 100.63%. Furthermore, in pure CNT-TCOTA, (FOM)1 and (FOM)2 have increased by 194% and 173%, respectively. It has also been investigated thoroughly how CNT-based OTAs perform by adjusting the CNT diameter (DCNT), pitch (S), and number of CNTs (N) at CL = 0.01 pF and 0.9 V power supply. It has been determined that using optimum CNT quantity, the pitch between CNTs, and diameter values can further enhance their performance. The simulation and comparative studies of all circuit structures have reported that novel and remarkable improvement is distinguished in CNT-based TCOTA. According to simulation and comparative assessments of all circuit structures, CNT-based TCOTA exhibits a novel and noteworthy improvement. Moreover, when compared to the conventional CMOS-TCOTA, the pure CNT-TCOTA has shown significant enhancement of 11.1% and 10.24% in GM and PM, respectively. Pure CNT-TCOTA has been demonstrated to be highly stable by the stability analysis.

Novel carbon nanotube field effect transistor based dual output second‐generation current conveyor: Design and applications

AbstractIn this work, we propose, design and simulate a new configuration of Class AB dual output (DO) second‐generation current conveyor (DO‐CCII). Two versions of this new DO‐CCII configuration are proposed: one employing 32 nm technology‐based carbon nanotube field effect transistor (CNTFET) and the other employing the conventional complementary MOS (CMOS). The HSPICE simulation studies have been performed to evaluate key performance parameters like current and voltage gains, voltage and current bandwidths (BW), the port X and Y resistances, total harmonic distortion of both proposed DO‐CCII configurations. It has been seen that ~388× and ~215× improvement in current and voltage BWs respectively have been achieved in the proposed CNTFET based DO‐CCII (CNTFET‐DO‐CCII) configuration in comparison to its CMOS counterpart (CMOS‐DO‐CCII). Similarly, desired port X and Y resistances have resulted substantially in the CNTFET based DO‐CCII configuration. Further, to evaluate the performance of proposed DO‐CCIIs, some applications such as sinusoidal oscillator, integrator and differentiator have been simulated and compared. In the designed oscillators, the effect of temperature on oscillating frequency has also been studied. A temperature insensitive behavior has been seen in the CNTFET‐DO‐CCII for a wide frequency range. Furthermore, it has been found that the optimization of number of CNTs, CNT diameter and inter‐CNT pitch of CNTFETs improve the performance of the proposed DO‐CCII.

Performance evaluation of SRAM design using different field effect transistors

SRAM (Static Random Access Memory) is one of the type of memory which holds the data bit without periodic refreshment. Compared with DRAM (Dynamic Random Access Memory) which requires periodic refreshment of data bit stored in it. Unlike Dynamic RAM, Static RAM uses a flip-flop circuit to store each data bit, whereas Dynamic RAM uses a capacitor to store the data bit. But capacitor has tendency of losing charge which requires periodic refreshment. Thus SRAM perform better and have more stability than DRAM especially in idle state. In this work, we analysed the performance of the SRAM cell which are built with different field effect transistors and calculated the Write and Read delays, PDP (Power Delay Product) and Static Noise Margin (SNM) for all types of transistors. SRAM cell which is based on the CNT technology with optimized parameters of CNT density, CNT diameter and CNTFET flat band voltage has the better performance and stability compared with other device technologies. Optimized CNTFET SRAM cell compared with the MOSFET based SRAM the write and read delays are improved by 85.8% and 94.3% respectively. All the simulations have been carried out using HSPICE tool for 32nm technology node.

Energy Efficient Circuit Design of Single Edge Triggered Ternary Shift Registers Using CNT Technology

With the miniaturization of digital integrated circuits, electronic systems with increased functionality and enhanced performance are preferred. Multi-valued logic design is a promising alternative that offers a higher number of data/information which leads to energy efficiency, higher information density and reduced circuit overheads in terms of interconnect complexity. Hence in this work multi-valued logic design benefits of increased computational capability and reduced interconnect complexity are being explored for the implementation of sequential elements viz. ternary shift registers. Carbon nanotube field-effect transistors(CNTFETs) unique feature of alteration of threshold voltage by variations in CNT diameter further favor its suitability to implement ternary logic designs. Here single-edge triggered ternary shift registers design methodology is presented using multiplexer based D-flip-flop cells. The design of D-flip-flops is performed using multiplexer based positive and negative latches. After this series connection of D-flip-flop is performed to construct serial input serial output and parallel input serial output registers. The parallel input serial output registers can operate in two modes of loading and shifting and three different configurations of AND-OR logic, NAND logic and latch based selection circuitry are proposed. For performance analysis Synopsis HSPICE simulations are conducted using the 32nm CNTFET Stanford model. According to simulation results, for the proposed ternary shift registers maximum reduction in power consumption and energy consumption of more than 80% are obtained as compared to recent counterparts.

Design of Ternary Logic Circuits using Pseudo N-type CNTFETs

In this paper, a novel method is presented to design ternary logic circuits for nanoelectronics applications. The ternary logic is a best alternative to the binary logic because it offers reduced interconnects, faster operating speed and reduced chip area. The digital logic circuit designs are developed using Pseudo N-type carbon nanotube field effect transistors (CNTFETs). The threshold voltage of CNTFETs is altered by the CNT diameter that is defined by the chirality vector. The ternary inverters such as standard inverter (SI), positive inverter (PI) and negative inverter (NI) and ternary basic gates such as AND, NAND, OR and NOR gates are designed. Furthermore, the half adder circuits developed which assists to develop complex circuit schematics. The proposed ternary schematics are designed and simulated using the HSPICE simulator. Moreover, the performance of the proposed circuits are investigated in terms of delay, power dissipation and power delay product (PDP) and compared with the existing circuits. It is observed that the proposed circuits show average performance improvement up to 47.48% over the existing circuits.

Vertically aligned carbon nanotubes for monovalent cation selective membranes designed by in silico experiments

Many membrane-based ion separation technologies require monovalent cations selectivity. However, available membranes usually show limited specific ion selectivity. In order to provide basic information on the membrane ion selectivity, the confinement effect on narrow pores disrupting the ion hydration is investigated in this work, with the aim to provide a new alternative to classical Cation Exchange Membranes (CEM). Starting from solvated cations structures used as templates and obtained by a quantum approach, Single-Wall Carbon Nanotubes (SWCNT) with ad-hoc designed diameters were chosen to perform in-silico experiments of single-cation permeation through CNT by means of Molecular Dynamics simulations, for which partial charges at nanotube inlets were parametrized through ab initio calculations. Cations' trajectories and energy decomposition analysis suggest that 100 % perm-selectivity towards Na+ with respect to Ca2+ and Mg2+ is virtually attainable with CNT of 1.33 nm diameter. Interestingly, the origin of this behaviour lays on thermodynamics rather than on size exclusion mechanisms. Opposite to polymeric homogeneous CEM, showing higher affinity for multivalent cations, an inverted trend was found for CNT in terms of hydration free energies, where Na+ shows more affinity up to 36 kJ/mol. Finally, total rejection of Cl− was observed in the range of CNT diameters investigated.

I-V Characteristics Modeling of the Carbon Nanotube Field Effect Transistor (CNTFET)

Abstract: A simulation model of a zig-zag type (10.0) single-walled carbon-nanotube (SW-CNT) transistor based on virtual source (VS-CNTFET) approach is presented in this paper. This semi-empirical physics-based model allowed the study of current-voltage (I-V) characteristics of the transistor. Additionally, analytical modeling of reflection coefficient, electron mobility in the CNT with low and high electric field and parasitic resistances (Rs and Rd) were presented as well in this model. Then, the obtained I-V characteristics of this SW-CNTFET were explored and compared with literature data obtained experimentally. Results showed that this model was a different approach which is significant compared to the silicon model in terms of the carrier mobility, where µCNT = 104 cm2/Vs. Moreover, the impacts of some geometric parameters, such as CNT length and diameter as well as oxide permittivity on the I-V characteristics, were proved. Keywords: Carbon nanotube, Virtual source, CNTFET, Electron mobility, I-V characteristics.

Probing the role of CNTs in Pt nanoparticle/CNT/graphene nanohybrids H2 sensors

In the carbon nanotubes film/graphene heterostructure decorated with catalytic Pt nanoparticles using atomic layer deposition (Pt-NPs/CNTs/Gr) H2 sensors, the CNT film determines the effective sensing area and the signal transport to Gr channel. The former requires a large CNT aspect ratio for a higher sensing area while the latter demands high electric conductivity for efficient charge transport. Considering the CNT’s aspect ratio decreases, while its conductivity increases (i.e., bandgap decreases), with the CNT diameter, it is important to understand how quantitatively these effects impact the performance of the Pt-NPs/CNTs/Gr nanohybrids sensors. Motivated by this, this work presents a systematic study of the Pt-NPs/CNTs/Gr H2 sensor performance with the CNT films made from different constituent CNTs of diameters ranging from 1 nm for single-wall CNTs, to 2 nm for double-wall CNTs, and to 10–30 nm for multi-wall CNTs (MWCNTs). By measuring the morphology and electric conductivity of SWCNT, DWCNT and MWCNT films, this work aims to reveal the quantitative correlation between the sensor performance and relevant CNT properties. Interestingly, the best performance is obtained on Pt-NPs/MWCNTs/Gr H2 sensors, which can be attributed to the compromise of the effective sensing area and electric conductivity on MWCNT films and illustrates the importance of optimizing sensor design.

Pressure-induced structural transformations on linear carbon chains encapsulated in carbon nanotubes: A potential route for obtaining longer chains and ultra-hard composites

In this paper, we report high-pressure Raman experiments (0 − 28 GPa) in two different systems, i.e., linear carbon chains encapsulated by multi-walled (Cn@MWCNTs) and double-walled (Cn@DWCNTs) carbon nanotubes. By running high-pressure cycles, it is observed basically two changes in the Raman spectra of chains that are the softening and disappearance of Cn modes. We attributed the irreversible redshift of the Cn band to the coalescence between adjacent chains. On the other hand, the disappearance of the Cn band at the onset of the CNT collapse pressure is assigned to the tube-chain cross-linking. This effect appears to be independent of the Cn length and the number of walls of the tubes, depending only on the innermost CNT diameter. We show that the pressure to coalesce longer chains is higher than 10 GPa. Density functional theory and molecular dynamics calculations were performed in order to support the interpretation of experimental data. The calculations show an irreversible pressure-induced softening of frequency of the confined linear carbon chain. Furthermore, molecular dynamics calculations showed that coalescence between the shorter chains occurs in a region of lower pressure than that of the longer chains, thus supporting the experimental observations. Our findings shed new light on the understanding of the Cn@CNT system stability and pave the way for using high-pressure to obtain ultra-long chains (at lower pressures) and ultra-hard composites (at higher pressures).

Impact of channel parameters on threshold voltage at variable temperatures of Double-gate CNTFET

This paper focuses mainly on the effect of various channel parameters like chirality, diameter of CNT, high-k dielectric materials and oxide layer thickness of DG-CNTFET on the threshold voltage at different temperature range of 225K–400K using nanoHUB simulation tools. The minor reductions (less than 5%) in threshold voltage of DG-CNTFET with respect to variable temperature increasing from 225K to 400K are observed. The results show that the threshold voltage increases with the reduction in carbon nanotube diameter of DG-CNTFET which affects the thermal conductivity of device as the van der Waals interaction between carbon-carbon bonds gets affected in DG-CNTFET. It was also investigated that decrease in quantum capacitance of DG-CNTFET improves the propagation delay of device. Using higher k-dielectric materials in DG-CNTFET enables faster switching speeds and lowers the power dissipation. Finally, based on results a conclusion has been drawn that best performance was recorded at lower value of temperature for threshold voltage.

Effect of reduction conditions of Mo-Fe/MgO on the formation of carbon nanotube in catalytic methane decomposition

The effects of temperature, hydrogen partial pressure, and time in catalytic reduction step on carbon nanotube growth in a catalytic methane decomposition have been investigated for Mo-Fe/MgO catalysts. The results show that the reduction conditions of the catalyst affect the crystal structure of the metal formed on the catalyst surface and the growth mechanism of the generated carbon nanotubes. Both diameter distribution and crystallinity of the CNTs increased with the increase of reduction temperature in the range of 400 to 800 °C. The optimal reduction temperature with the maximum carbon yield was found to be 500 °C. The increase of hydrogen partial pressure and reduction time increased the CNT diameter distribution, and the optimal hydrogen partial pressure and reduction time with maximum carbon yield were found to be 0.1 atm, 60 min and 0.3 atm, 5 min, respectively. In the different combination of hydrogen partial pressure and reduction time for maximizing carbon yield, the CNT average diameter did not have a significant change, while the CNT crystallinity showed opposite trends depending on the methane decomposition reaction time. Ultimately, it was confirmed that the Mo-Fe/MgO catalyst can change the properties of CNTs produced through control of reduction conditions.

Hybrid composite materials generated via growth of carbon nanotubes in expanded graphite pores using a microwave technique

Herein we demonstrate a facile in-situ synthesis method by selection of expanded graphite as a matrix growth microreactor, nickel nitrate (Ni(NO3)2) as a growth catalyst and naphthalene as a carbon source, assisted by a conventional household microwave oven. Affection parameters related to control of the growth process, such as the microwave heating time, catalyst concentration and carbon source concentration. The optimized experimental conditions that exhibit excellent microstructure were: a carbon source concentration of 20.0 mg/ml, a catalyst concentration of 10.0 mg/ml and a microwave reaction time of 30 s. The microstructure of the synthesized composites was investigated and a solid-gas growth mechanism with this carbon source precursor is proposed. The micro morphology, formed CNT structure and resistivity of the composites are fully characterized and analyzed by thermal field emission high-resolution scanning electron microscopy (FESEM), confocal laser Raman spectrometer (Raman) and a four-point probe resistivity meter. All characterization data show a uniform CNT diameter distribution of approximately 30.0 nm with a low resistivity of the composites (1.12 × 10−5 Ω·m), indicating uniform hybrid composite material formation with novel physical properties.

Optimizing CNTFET design parameters using Taguchi method for high performance and low power applications

The features of CNT (Nanotube Carbon) are fascinating to study due to their unique structural and electrical capabilities. The small structure of the CNT in Field-Effect Transistor technology can produce a smaller device with a better performance. In this work, the Taguchi method had been implemented to optimize the Carbon Nanotube Field-Effect Transistor (CNTFET). The Minitab 19 software had been used to carry out the Taguchi method analysis. Three design parameters (diameter of CNT, pitch and the number of CNT) with three different sizes each had been chosen to improve the CNTFET capabilities. L27 orthogonal array and signal-to-noise (SNR) was used to collect and analyze the data. The result from the Taguchi method was validated by using ANOVA. The analysis results displayed the best combination of the three design parameters that produce the optimum performance in terms of high power and low power application. The study showed that the most dominant design parameter that affects the CNTFET’s current characteristics is the diameter of CNT with 59.93%, 96.15% and 99.14% towards on-current (Ion), off-current (Ioff) and current ratio (Ion/Ioff), respectively. By identifying the most dominant structure in CNTFET, the device can be further optimized. Eventually, the CNTFET devices in terms of high power and low power application can be enhanced.

Key factors for ultra-high on/off ratio thin-film transistors using as-grown carbon nanotube networks.

Approximately 30% of as-grown carbon nanotube (CNT) networks are metallic, usually leading to a trade-off between carrier mobility and on/off ratio in CNT thin-film transistors (TFTs). Figuring out the key factors of ultra-high on/off ratio in CNT TFTs should be considerably essential for the development of large-scale electronic devices in the future. Here ultra-high on/off ratios of 107–108 are realized for CNT TFTs with mobility of ∼500 cm2 V−1 s−1. We propose that one of the key factors to achieve the high on/off ratio is a clean CNT thin film without charge traps and doping due to residual dispersant used in conventional solution processes. Moreover, on/off ratio degradation under operation voltage is significantly suppressed by decreasing the diameter of CNTs.