Single-walled Carbon Nanotube Thin-film Transistors Research Articles

Diameter distribution control of single-walled carbon nanotubes by etching ferritin nanoparticles

We focused on controlling the diameter of single-walled carbon nanotubes (SWNTs) by controlling the ferritin catalyst diameter using reactive ion etching (RIE). The average diameter of ferritin decreased by about 26.5% upon RIE treatment, which resulted in the decrease of the mean diameter of the SWNTs by about 34% with a small diameter distribution. This was demonstrated by both atomic force microscopic and Raman spectroscopic measurements. We found that the current on/off ratio of the SWNT thin film transistors was significantly improved after the catalyst treatment. It was estimated that the purity of the semiconducting SWNT also increased from 58.8 to 92.4%.

Subnanowatt Carbon Nanotube Complementary Logic Enabled by Threshold Voltage Control

In this Letter, we demonstrate thin-film single-walled carbon nanotube (SWCNT) complementary metal-oxide-semiconductor (CMOS) logic devices with subnanowatt static power consumption and full rail-to-rail voltage transfer characteristics as is required for logic gate cascading. These results are enabled by a local metal gate structure that achieves enhancement-mode p-type and n-type SWCNT thin-film transistors (TFTs) with widely separated and symmetric threshold voltages. These complementary SWCNT TFTs are integrated to demonstrate CMOS inverter, NAND, and NOR logic gates at supply voltages as low as 0.8 V with ideal rail-to-rail operation, subnanowatt static power consumption, high gain, and excellent noise immunity. This work provides a direct pathway for solution processable, large area, power efficient SWCNT advanced logic circuits and systems.

Low voltage, high performance inkjet printed carbon nanotube transistors with solution processed ZrO2 gate insulator

High-performance single-walled carbon nanotube (SWCNT) thin-film transistors are fabricated by single-pass inkjet printing of SWCNTs on high-κ solution-processed ZrO2 gate dielectric. We demonstrate that an ultraviolet ozone treatment of the ZrO2 substrate is critical in achieving a uniform dispersion of sorted SWCNTs in the semiconducting channel. The resulting devices exhibit excellent performance with mobility and on/off current ratio exceeding 30 cm2 V−1 s−1 and 105, respectively, at low operating voltages (<5 V). The single-pass inkjet printing process demonstrated in this letter shows great promise as a reliable and scalable method for SWCNT based high performance electronics.

Thin-Film Transistor Using Dielectrophoretic Assembly of Single-Walled Carbon Nanotubes

A single-walled carbon nanotube thin-film transistor (SWNT TFT) was formed using aligned SWNT channels assembled by the dielectrophoretic (DEP) process. The density of assembled SWNTs was controlled by the DEP factors (concentration of SWNT solution and applied AC voltage). The on/off current ratio of the SWNT TFT was improved by decreasing the SWNT density in a channel, and it achieved 3.4×105. DEP assembly is an effective method to achieve well-aligned and density-controlled SWNT channels for TFT applications.

Thin-Film Transistors Using Uniform and Well-Aligned Single-Walled Carbon Nanotubes Channels by Dielectrophoretic Assembly

A single-walled carbon nanotube thin-film transistor (SWCNT TFT) was formed by an aligned SWCNTs channel assembled by the dielectrophoretic (DEP) process. In this work, we investigated the effects of the DEP factors (frequency, solution concentration) on structural (orientation and density in the SWCNT channels) and electrical properties of SWCNT TFTs. A uniform, well-aligned and density controlled SWCNT channel was achieved by optimizing the DEP assembly process, and as a result, electrical properties (mobility and on/off current ratio) of SWCNT TFTs were improved. In addition, we also discussed the effect of uniformity of assembled SWNTs in a channel on performance variation of the SWCNT TFTs. We found that the tube density and uniformity are key parameters which determine electrical properties and performance variation of SWCNT TFTs.

Carbon Nanotubes for Thin Film Transistor: Fabrication, Properties, and Applications

We review the present status of single‐walled carbon nanotubes (SWCNTs) for their production and purification technologies, as well as the fabrication and properties of single‐walled carbon nanotube thin film transistors (SWCNT‐TFTs). The most popular SWCNT growth method is chemical vapor deposition (CVD), including plasma‐enhanced chemical vapor deposition (PECVD), floating catalyst chemical vapor deposition (FCCVD), and thermal CVD. Carbon nanotubes (CNTs) used to fabricate thin film transistors are sorted by electrical breakdown, density gradient ultracentrifugation, or gel‐based separation. The technologies of applying CNT random networks to work as the channels of SWCNT‐TFTs are also reviewed. Excellent work from global researchers has been benchmarked and analyzed. The unique properties of SWCNT‐TFTs have been reviewed. Besides, the promising applications of SWCNT‐TFTs have been explored. Finally, the key issues to be solved in future have been summarized.

Fully Gravure-Printed Flexible Full Adder Using SWNT-Based TFTs

A single-walled carbon nanotube (SWNT)-based 1-b full-adder circuit was realized on flexible plastic substrates through an all gravure printing process by minimizing intertransistor process variation and leakage current between crossing interconnects. The circuit comprised 27 printed SWNT thin-film transistors, with a variation of up to only ±25% in electrical characteristics among them. Furthermore, the circuit showed a maximum propagation delay of 13.7 ms, with a 50-Hz input signal, and a supply voltage of -20 V. The process could be used for low-cost flexible arithmetic logic units in a variety of applications.

Length-dependent performances of sodium deoxycholate-dispersed single-walled carbon nanotube thin-film transistors

Abstract

Charge Injection in High-κ Gate Dielectrics of Single-Walled Carbon Nanotube Thin-Film Transistors

We investigate charge injection into the gate dielectric of single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) having Al(2)O(3) and HfO(2) gate dielectrics. We demonstrate the use of electric field gradient microscopy (EFM) to identify the sign and approximate the magnitude of the injected charge carriers. Charge injection rates and saturation levels are found to differ between electrons and holes and also vary according to gate dielectric material. Electrically, Al(2)O(3) gated devices demonstrate smaller average hysteresis and notably higher average on-state current and p-type mobility than those gated by HfO(2). These differences in transfer characteristics are attributed to the charge injection, observed via EFM, and correlate well with differences in tunneling barrier height for electrons and holes formed in the conduction and valence at the SWCNT/dielectric interface, respectively. This work emphasizes the need to understand the SWCNT/dielectric interface to overcome charge injection that occurs in the focused field region adjacent to SWCNTs and indicates that large barrier heights are key to minimizing the effect.

Inkjet printing of single-walled carbon nanotube thin-film transistors patterned by surface modification

In this paper, we report a method for the inkjet printing of single-walled carbon nanotube thin-film transistors (SWCNT TFTs). Although inkjet technology is a powerful tool for the fabrication of SWCNT TFTs, the diameter of the ink droplets (100 μm) strictly limits the device size. Here, we surmount this limitation by combining inkjet technology and site-selective deposition based on the patterning of self-assembled monolayers. We have synthesized patterned SWCNT films with feature widths less than 100 μm using this site-selective surface modification method, thus improving the performance limit of SWCNT printed electronics.

Diameter‐Dependent Performance of Single‐Walled Carbon Nanotube Thin‐Film Transistors

Single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) with various tube diameters and constant tube length are investigated. Similar variations of on-currents, independent of the diameter, are demonstrated according to percolation theory, but off-currents significantly depend on the diameter. The temperature dependence of the off-currents attributes the observed non-negligible off-state conductance to thermally excited carriers in semiconducting SWCNTs.

Total ionizing dose-hardened carbon nanotube thin-film transistors with silicon oxynitride gate dielectrics

We investigate the radiation response of single-walled carbon nanotube (SWCNT) thin-film transistors fabricated with 23 nm silicon oxynitride gate dielectric layers, for total ionizing doses (TIDs) of Co-60 gamma irradiation up to 2 Mrad(Si). Irradiations with ±1 MV/cm across the gate dielectric have little effect on the threshold voltage, yielding shifts of less than ±0.25 V and no detrimental effect on SWCNT mobility or maximum drain current. This illustrates the need to consider the total device material composition when investigating the radiation response of carbon nanoelectronics and substantiates the applicability of SWCNT-based nanoelectronics for use in high TID environments.

Single-Walled Carbon Nanotube Thin Film Transistor Fabricated Using Solution Prepared with 9,9-Dioctyfluorenyl-2,7-diyl–Bipyridine Copolymer

Performance of thin film transistor (TFT) whose channel is fabricated by using a solution process of single-walled carbon nanotube (SWCNT) has been studied. SWCNT solution is prepared by using 9,9-dioctyfluorenyl-2,7-diyl–bipyridine (PFO–BPy) copolymer as solubilizer. Over 4 decades' on/off ratio is obtained by using drop-coating at room temperature without any further optimization. Other solubilizers are chosen as control groups to measure the on/off ratio of SWCNT TFT to investigate effects of the use of PFO–BPy. Results suggest that thick SWCNT network should be uniformly established at the channel region and the channel is required to be formed with well-separated SWCNTs.

Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips

The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel formation. The transistors are manufactured on oxidized silicon wafers and flexible plastic substrates at ambient conditions. For this purpose, ink-jet printing techniques are developed with the aim of high-throughput production of SWCNT thin-film channels shaped in long strips. Stable SWCNT inks with proper fluidic characteristics are formulated by polymer addition. The present work unveils, through Monte Carlo simulations and in light of heterogeneous percolation, the underlying physics of the superiority of long-strip channels for SWCNT TFTs. It further predicts the compatibility of such a channel structure with ink-jet printing, taking into account the minimum dimensions achievable by commercially available printers. The printed devices exhibit improved electrical performance and scalability as compared to previously reported ink-jet printed SWCNT TFTs. The present work demonstrates that ink-jet printed SWCNT TFTs of long-strip channels are promising building blocks for flexible electronics.

High yield production of semiconducting p-type single-walled carbon nanotube thin-film transistors on a flexible polyimide substrate by tuning the density of ferritin catalysts

We report on a simple method for fabricating pure p-type single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) on flexible polyimide substrates without selective removal of metallic SWCNTs from the as-grown CNT films. The density of the SWCNTs was controlled by tuning the concentration of ferritin catalyst, resulting in the control of the metallic percolation pathways in the SWCNT TFTs. For a ferritin solution diluted by 1/2000, approximately 60% of the pristine SWCNT TFTs showed p-type behavior with larger on/off current ratios, ( I on/ I off > 10 4) and a high photosensitivity to the exposure of UV/visible light.

Radiation Effects in Single-Walled Carbon Nanotube Thin-Film-Transistors

The fabrication, characterization, and radiation response of single-walled carbon nanotube (SWCNT) thin-film field effect transistors (SWCNT-TFTs) has been performed. SWCNT-TFTs were fabricated on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -Si substrates from 98% pure semiconducting SWCNTs separated by density gradient ultracentrifugation. Optical and Raman characterization, in concert with measured drain current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> ratios, up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> , confirmed the high enrichment of semiconducting-SWCNTs. Total ionizing dose (TID) effects, up to 10 MRads, were measured in situ for a SWCNT-TFT under static vacuum. The results revealed a lateral translation of the SWCNT-TFT transfer characteristics to negative gate bias resulting from hole trapping within the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -SWCNT interface. Additional TID exposure conducted in air on the same device had the opposite effect, shifting the transfer characteristics to higher gate voltage, and increasing the channel conductance. No significant change was observed in the device mobility or the SWCNT Raman spectra following a TID exposure of 10 Mrad(Si), indicating extrinsic factors dominate the transfer characteristics in the SWCNT-TFT devices during irradiation. The extrinsic effects of charge trapping and the role that gas adsorption plays in the radiation response are discussed.

Optimization of single-walled carbon nanotube growth and study of the hysteresis of random network carbon nanotube thin film transistors

Random network single-walled carbon nanotube (SWNT)-based thin film transistors show excellent properties in sensors, electronic circuits, and flexible devices. However, they exhibit a significant amount of hysteresis behavior, which should be solved prior to use in industrial applications. This paper provides optimum conditions for the growth of random network SWNTs and reveals that the observed hysteresis behavior originates from the charge exchange between the SWNTs and the dielectric layer rather than from changes in the intrinsic properties of the SWNTs. This was proven by studying the conditions of stepwise gate sweep experiments and time measurements. This paper also shows that top gate SWNT thin film transistors (TFTs) with an SU-8 dielectric layer could provide a practical solution to the hysteresis problem for SWNT TFTs in electronic circuit applications.

Effects of UV light and carbon nanotube dopant on solution-based indium gallium zinc oxide thin-film transistors

We studied the effects of ultraviolet (UV) light and the electrical properties of solution-based indium gallium zinc oxide single-walled carbon nanotube thin-film transistors ( SB-IGZO/SWNT TFT), compared with those of solution-based IGZO TFT. Of these devices, the SB-IGZO/SWNT TFT had excellent photo-induced current-sensitivity under illumination and significantly slower recovery of the transfer characteristics after switching off the UV light. To explain these unique photo-response behaviors, we believe that SWNTs play an important role as carrier transport rods during device operation and as electron traps in the device off-state, along with electron–hole pairs due to the UV light illumination.

A low voltage operational single-walled carbon nanotube thin-film transistor containing a high capacitance gate dielectric layer produced by layer-by-layer deposition

This paper presents the characteristics of a low voltage driven thin-film transistor (TFT) containing an active layer coated with a single-walled carbon nanotube (SWCNT) network. To make the high capacitance gate dielectrics layers, poly(ethylene imine) and the titanium oxide precursor, titanium(IV) bis(ammonium lactate) dihydroxide, were coated by a layer-by-layer deposition method. Through this process we obtained a capacitance of 118 nF/cm 2 and a total thickness of about 70 nm. The SWCNT active layer was deposited by spray-coating onto the layered-gate dielectric using a solution containing purified SWCNTs and a polystyrene additive. We used polystyrene in the coating solution to increase the dispersion of SWCNTs in the 1-methyl-2-pyrrolidone solution and decrease current leakage though the TFT channels. The resulting TFT showed a mobility of 6.7 cm 2/V s, a threshold voltage of −0.88 V, and an on/off ratio of about 500 at operating voltages less than 2 V, which is suitable for the operation of various portable electronic devices. The output characteristics showed a good linear character and well-saturated behavior at elevated drain voltage.

Low-Voltage Operation of Ink-Jet-Printed Single-Walled Carbon Nanotube Thin Film Transistors

We demonstrate a low-voltage and less hysteresis operation of single-walled carbon nanotube thin film transistors (SWCNT-TFTs) using an ionic liquid gate dielectric layer. We fabricated the density controlled SWCNT-TFTs using the inkjet printing technique, where both source/drain electrodes and the semiconducting transistor channel were made from SWCNT films. As the gate dielectric, we have adopted a printable ionic liquid for future all-printable processes and achieved marked improvements in operating voltages and hysteretic response.