Single-walled Carbon Nanotube Thin-film Transistors Research Articles

High-sensitivity and energy-efficient chloride ion sensors based on flexible printed carbon nanotube thin-film transistors for wearable electronics

The advent of flexible single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) has transformed electronics, providing significant benefits like low operating voltage, reduced power consumption, cost-effectiveness, and improved signal amplification. This study focuses on leveraging these attributes to develop a novel flexible high-sensitivity and energy-efficient chloride ion sensors based on printed flexible SWCNT-TFTs utilizing polymers-sorted semiconducting SWCNTs (sc-SWCNTs) as the active layers and ion liquids-poly(4-vinylphenol as dielectric layers along with the evaporated deposition of aluminum electrodes and printed silver electrodes as the gate and source-drain electrodes, respectively. The sensors exhibit several operational advantages, including low voltage requirements (≤1 V), rapid response speed (5.32 s), significant signal amplification (Up to 702.6 %), low power consumption (0.31 μJ at 1 mmol chloride ion), good repeatability, high sensitivity for both low and high concentrations of chloride ion (up to 100 mmol/L) and excellent mechanical flexibility (No obvious changes after bending for 10,000 times with a 5 mm radius). The detection mechanism of chloride ions was analyzed using X-ray Photoelectron Spectroscopy (XPS). It was found that chloride ions react with silver nanoparticles (AgNPs) to form silver chloride (AgCl) on printed electrodes, impeding carrier transport and reducing the currents in SWCNT TFTs. Importantly, our sensors' compatibility with smart devices allows for real-time monitoring of chloride ion levels in human sweat, offering significant potential for daily health monitoring.

Optimum Design Configuration of Thin-Film Transistors and Quantum-Dot Light-Emitting Diodes for Active-Matrix Displays.

Active matrix (AM) quantum-dot light-emitting diodes (QLEDs) driven by thin-film transistors (TFTs) have attracted significant attention for use in next-generation displays. Several challenges remain for the realisation of AM-QLEDs, such as device design, fabrication process, and integration between QLEDs and TFTs, depending on their device structures and configurations. Herein, efficient and stable AM-QLEDs are demonstrated using conventional and inverted structured QLEDs (C- and I-QLEDs, respectively) combined with facile type-convertible (p- and n-type) single-walled carbon nanotube (SWNT)-based TFTs. Based on the four possible configurations of the QLED-TFT subpixel, the performance of the SWNT TFT-driven QLEDs and the fabrication process to determine the ideal configuration are compared, taking advantage of each structure for AM-QLEDs. The QLEDs and TFTs are also optimized to maximise the performance of the AM-QLEDs-the inner shell composition of quantum dots and carrier type of TFTs-resulting in a maximum external quantum efficiency and operational lifetime (at an initial luminance of 100cdm2 ) of 21.2% and 38 100 000h for the C-QLED, and 19.1% and 133100000h for the I-QLED, respectively. Finally, a 5×5 AM-QLED display array controlled using SWNT TFTs is successfully demonstrated. This study is expected to contribute to the development of advanced AM-QLED displays.

Fully solution-processed carbon nanotubes thin film transistors and PMOS inverters on glass substrate

We report fully solution-processed thin film transistors and PMOS inverters fabricated on glass substrates using single-walled carbon nanotubes (SWCNTs) as active semiconducting material. All the electrodes (gate, source, and drain) were inkjet-printed using silver (Ag) as conductive ink. Spin coated poly-4-vinylphenol dielectric was optimized in terms of thickness and heating conditions for solution-processed SWCNTs thin film transistors to achieve a mobility equal to 0.81 cm2 V−1s−1. We will show that, hole traps at the dielectric-semiconductor interface are responsible for the hysteresis in the transfer curve, and controlled by the different sweep rate of the gate field. Drain-current transients under different bias conditions were studied and the increase in current occurs due to slow polarizations of residual dipolar groups in the dielectric. The adopted technology has been exploited to fabricate a PMOS inverter and studied for high gain and noise margin values at the supply voltage, V DD = −40 V.

Fully-Solution-Processed Enhancement-Mode Complementary Metal-Oxide-Semiconductor Carbon Nanotube Thin Film Transistors Based on BiI3 -Doped Crosslinked Poly(4-Vinylphenol) Dielectrics for Ultralow-Power Flexible Electronics.

The threshold voltage (Vth ) adjustment of complementary metal-oxide-semiconductor (CMOS) thin film transistors (TFTs) is one of the research hotspotsdue to its key role in energy consumption control of CMOS circuits. Here, ultralow-power flexible CMOS circuits based on well-matched enhancement-mode (E-mode) CMOS single-walled carbon nanotube (SWCNT) TFTs are successfully achieved through tuning the work function of gate electrodes, electron doping, and printing techniques. E-mode P-type CMOS SWCNT TFTs with the full-solution procedure are first obtained through decreasing the work function ofAg gate electrodes directly caused by the deposition of bismuth iodide(BiI3 )-doped solid-state electrolyte dielectrics. After synthetic optimization of dielectric compositions and semiconductor printing process, the flexible printed E-mode SWCNT TFTs show the high Ion /Ioff ratios of ≈106 , small subthreshold swing (SS) of 70-85mV dec-1 ,lowoperating voltages of ≈0.5 to -1.5V, good stabilityand excellent mechanical flexibility during 10000 bending cycles. E-mode N-type SWCNT TFTs are then selectively achieved via printing the polarity conversion ink (2-Amino-2-methyl-1-propanol (AMP) aselectron dopingagent) in P- type TFT channels. Last, printed SWCNT CMOS invertersare successfully constructed with full rail-to-rail output characteristics and the record unit static power consumption of 6.75 fW µm-1 at VDD of 0.2V.

Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications

We report daylight-stable, transparent, and flexible single-walled carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet printing process. Although most of the previous reports classified SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually show two different types of photoresponses depending on the power levels of light sources. The electrical characteristics of SWCNT TFTs show no significant change under daily illumination conditions such as halogen lamps and sunlight, while under high-power laser illumination, they change as reported in the previous results. In addition, the low-temperature solution process of the SWCNT with its one-dimensional nature allows us to realize highly transparent and flexible TFTs and logic circuits on plastic substrates. Our result will provide new insights into utilizing SWCNT TFTs for light-insensitive transparent and flexible electronic applications.

Resolving the Unusual Gate Leakage Currents of Thin-Film Transistors with Single-Walled Carbon-Nanotube-Based Active Layers

Solution-processed single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) in the research stage often have large active areas. This results in unusual gate leakage currents with high magnitudes that vary with applied voltages. In this paper, we report an improved structure for solution-processed SWCNT-based TFTs. The unusual gate leakage current in the improved structure is resolved by patterning the SWCNT active layer to confine it to the channel region. For comparative purposes, this improved structure is compared to a traditional structure whose unpatterned SWCNT active layer expands well beyond the channel region. As TFT performance also varies with oxide layer thickness, 90 nm and 300 nm thick oxides were considered. The improved TFTs have gate leakage currents far lower than the traditional TFT with the same dimensions (aside from the unpatterned active area). Moreover, the unusual variation in gate leakage current with applied voltages is resolved. Patterning the SWCNT layer, increasing the oxide thickness, and reducing the top electrode length all help prevent a rapid dielectric breakdown. To take advantage of solution-based fabrication processes, the active layer and electrodes of our TFTs were fabricated with solution-based depositions. The performance of the TFT can be further improved in the future by increasing SWCNT solution incubation time and reducing channel size.

Printed carbon nanotube thin film transistors based on perhydropolysilazane-derived dielectrics for low power flexible electronics

Electric double layer (EDL) electrolyte dielectrics have attracted great interest for low voltage and low power consumption portable thin film transistor (TFT) devices and circuits due to their high gate modulation efficiency. In this work, fully printed single-walled carbon nanotube (SWCNT) TFTs are fabricated using proton conducting inorganic perhydropolysilazane (PHPS) derivatives as the EDL dielectrics at low frequencies (<1 kHz) that can be processed in humidity even at quite low temperature (<100 °C) and relatively short reaction time (∼10 min). Fabricated fully printed SWCNT TFTs exhibit excellent electrical properties with low operating voltage (±1 V), high on/off ratio (∼106), small subthreshold swing (70–110 mV/dec), good stability and the average carrier mobility of 6.3 cm2 V−1 s−1. In addition, the precise control of the SWCNT TFTs’ threshold voltage and polarity (from depleted p-type to enhanced p and n-type, and well-balanced ambipolar) is successful demonstrated by adjusting the printable sc-SWCNT ink concentrations and electron doping technology (using ethanolamine as the electron doping agent). Furthermore, fully printed flexible complementary metal oxide semiconductor (CMOS) and CMOS-like inverters based on as-prepared SWCNT TFTs represent extremely low static power consumption (0.1 pW/μm and 0.05 pW/μm, respectively), high voltage gain (up to 45 at VDD = 0.7 V) and relatively large noise margins.

Fully roll-to-roll gravure printed 4-bit code generator based on p-type SWCNT thin-film transistors

Current Si-based technologies have reached their intrinsic limits in meeting the demands of flexible electronics where free-form factors and low cost are critical for successful applications. For this reason, roll-to-roll (R2R) gravure printing has been considered a way to achieve the free-form factor and the low cost. However, the R2R gravure systems (servomechanism, electronic ink, printing process, and device design) could not integrate a number of thin-film transistors (TFTs) with small threshold voltage (V th) variations. Therefore, we designed a 4-bit code generator by combining one ring oscillator, six NAND gates, and one OR gate based on 37 p-type single-walled carbon nanotube (SWCNT) TFTs as a concept devices to test the R2R gravure system. First, ring oscillators with different physical dimensions were printed on a poly (ethylene terephthalate) roll using the R2R gravure. Then, we extracted important factors (channel length, channel width, and SWCNT network density) to optimize the V th variation and demonstrated a 4-bit code generator integrated with 37 p-type TFTs. This work will be further extended in the near future to develop R2R gravure printed near-field communication labels for smart packaging.

Excess Polymer in Single-Walled Carbon Nanotube Thin-Film Transistors: Its Removal Prior to Fabrication Is Unnecessary.

Ultrapure semiconducting single-walled carbon nanotube (sc-SWNT) dispersions produced through conjugated polymer sorting are ideal candidates for the fabrication of solution-processed organic electronic devices on a commercial scale. Protocols for sorting and dispersing ultrapure sc-SWNTs with conjugated polymers for thin-film transistor (TFT) applications have been well refined. Conventional wisdom dictates that removal of excess unbound polymer through filtration or centrifugation is necessary to produce high-performance TFTs. However, this is time-consuming, wasteful, and resource-intensive. In this report, we challenge this paradigm and demonstrate that excess unbound polymer during semiconductor film fabrication is not necessarily detrimental to device performance. Over 1200 TFT devices were fabricated from 30 unique polymer-sorted SWNT dispersions, prepared using two different alternating copolymers. Detailed Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) studies of the random-network semiconductor films demonstrated that a simple solvent rinse during TFT fabrication was sufficient to remove unbound polymer from the sc-SWNT films, thus eliminating laborious polymer removal before TFT fabrication. Furthermore, below a threshold polymer concentration, the presence of excess polymer during fabrication did not significantly impede TFT performance. Preeminent performance was achieved for devices prepared from native polymer-sorted SWNT dispersions containing the "original" amount of excess unbound polymer (immediately following enrichment). Lastly, we developed an open-source Machine Learning algorithm to quantitatively analyze AFM images of SWNT films for surface coverage, number of tubes, and tube alignment.

Flexible printed single-walled carbon nanotubes olfactory synaptic transistors with crosslinked poly(4-vinylphenol) as dielectrics

Flexible brain-inspired neuromorphic transistors are spring up in the scopes of artificial electronic skins and human-interactive electronics for wearable devices and robotic applications benefiting from the capability of synchronous recognition and processing of the external information. In this work, we reported the flexible printed single-walled carbon nanotube (SWCNT) synaptic thin film transistors (TFTs) with printed silver electrodes as source/drain and gate electrodes, and the solid state electrolyte blending ionic liquids with crosslinked-poly(4-vinylphenol) (c-PVP) as dielectric layers. Our flexible printed SWCNT synaptic transistors display excellent electrical properties, such as low operation voltages (between ±1 V), high on/off ratios (>106) and low off currents (∼10−12 A), as well good stability and good mechanical flexibility. These flexible printed SWCNT TFT devices can imitate some typical synaptic plasticities like excitatory postsynaptic current and paired-pulse facilitation. The results indicate that synaptic behaviors of flexible devices are related to weight concentrations of ionic liquids in ionic c-PVP insulators. Moreover, our synaptic transistors can imitate the olfactory neurons and show the inhibitory characteristic when triggered by under a series of electrical stimulations after exposure to NH3.

Fabrication of Carbon Nanotube Thin Films for Flexible Transistors by Using a Cross-Linked Amine Polymer.

Owing to their remarkable properties, single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) are expected to be used in various flexible electronics applications. To fabricate SWCNT channel layers for TFTs, solution-based film formation on a self-assembled monolayer (SAM) covered with amino groups is commonly used. However, this method uses highly oxidized surfaces, which is not suitable for flexible polymeric substrates. In this work, a solution-based SWCNT film fabrication using methoxycarbonyl polyallylamine (Moc-PAA) is reported. The NH2 -terminated surface of the cross-linked Moc-PAA layer enables the formation of highly dense and uniform SWCNT networks on both rigid and flexible substrates. TFTs that use the fabricated SWCNT thin film exhibited excellent performance with small variations. The presented simple method to access SWCNT thin film accelerates the realization of flexible nanoelectronics.

Multidipping Technique for Fabrication Time Reduction and Performance Improvement of Solution‐Processed Single‐Walled Carbon Nanotube Thin‐Film Transistors

Herein, a simple and effective technique, “multidipping technique,” is implemented to rapidly form random networks of single‐walled carbon nanotubes (SWCNTs) used as a channel material in solution‐processed thin‐film transistors (TFTs). The multidipping process consists of repetition of dipping a substrate into a dispersed semiconducting SWCNT solution and rinsing the substrate between each dipping process. Compared with the conventional dipping method, this technique reduces total deposition time required to form high‐quality SWCNT networks by more than half and simultaneously improves the electrical performances of SWCNT TFTs. These phenomena are also comprehensively analyzed with experiments and microscopic images of the channel region, which well show morphology of the SWCNT networks. It is believed that the low‐temperature process and facile deposition method of SWCNT networks can provide a guideline for high‐throughput fabrication of high‐performance SWCNT TFT arrays in flexible active matrix sensor array and display applications.

An Ultra‐Flexible Solution‐Processed Metal‐Oxide/Carbon Nanotube Complementary Circuit Amplifier with Highly Reliable Electrical and Mechanical Stability

AbstractHere, high‐performance flexible complementary metal‐oxide–semiconductor (CMOS) amplifiers with extremely stable electro‐mechanical characteristics by employing low‐temperature solution‐processed amorphous indium–gallium–zinc oxide (a‐IGZO) and single‐walled carbon nanotube (SWCNT) thin film transistors (TFTs) is demonstrated. The photochemical‐activated combustion sol–gel a‐IGZO and SWCNT TFTs show average saturation mobility of 6.82 and 0.51 cm2 V−1 s−1, respectively. Based on the devices, a‐IGZO/SWCNT‐based CMOS amplifiers are implemented on ultrathin and flexible substrates (thickness of ≈3 µm), exhibiting small‐signal gain and unity‐gain bandwidth of up to 25 dB and 25 kHz, respectively, with highly reliable characteristics from 1000 bending stress (radius of 125 µm) and positive gate bias stress conditions (for up to 3 h). The underlying mechanisms of the CMOS performance combined with large output impedance of the SWCNT load are investigated in detail via various circuit implementations and automatic integrated circuit modeling Spice simulation and comprehensive electrical analysis. To ensure the viability of the extremely stable electromechanical properties of the flexible amplifier, a numerical analysis is carried out based on finite‐element methods with an integrated circuit emphasis to find the best match of the CMOS architecture and optimized structural integrity, verifying highly reliable and scalable skin‐like electronics.

Overcoming Electrochemical Instabilities of Printed Silver Electrodes in All-Printed Ion Gel Gated Carbon Nanotube Thin-Film Transistors.

Silver ink is the most widely used conductive material for printing electrodes in the fabrication of all-printed ion gel gated transistors because of their high conductivity and low cost. However, electrochemical instability of printed silver electrodes is generally one of the biggest issues, whether it is in air where silver gets oxidized or in a moisture environment where electrochemical migration occurs. Notwithstanding, the electrochemical stability of printed silver electrodes in ion gel medium has not been studied so far. In this work, we studied the electrochemical instabilities of printed silver electrodes in fully printed ion gel gated single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) and developed some strategies to overcome these issues. All-printed ion gel-based p-type SWCNT TFTs were employed to investigate the impact of electrochemical instabilities on the electrical behavior of printed SWCNT TFTs. The results have demonstrated that printed silver was unstable at anodic and cathodic polarization because of the corrosion by the ionic liquid. Besides, anodic corrosion of silver source/drain electrodes was shown to be responsible for the electrical failure of printed SWCNT TFTs in both the linear and saturated regime. These issues were completely resolved when preventing printed silver electrodes from coming into direct contact with ion gels. For example, ion gels were partially printed in device channels to avoid contacting the printed silver source and drain electrodes. At the same time, silver side-gate electrodes were replaced by inkjet-printed PEDOT:PSS electrodes to avoid gate electrode-related instabilities. Consequently, all-printed electrochemically stable SWCNT TFTs fabricated were obtained with enhanced performance of higher ION/IOFF ratios (105 to 106), smaller subthreshold slopes (∼70 mV/dec), and smaller hysteresis (ΔV = 0.025 V) at gate voltages from 1.2 to -0.5 V. Additionally, the polarity of all-printed SWCNT TFTs was converted from the p-channel to ambipolar while achieving lower leakage currents.

Radiation effects in printed flexible single-walled carbon nanotube thin-film transistors

In this study, the gamma ray radiation effect on the characteristics of inkjet-printed semiconducting single-walled carbon nanotubes (sSWCNTs) thin-film transistors (TFTs) is investigated. The devices with top gate dielectrics consisted of BaTiO3 and poly(methyl methacrylate) (PMMA) were characterized before and after 150 krad 60Co gamma radiation in air. It reveals that the radiation results in a positive threshold voltage shift from -0.5 to 3.6 V (with a drain voltage biased at -1 V). The hysteresis decreases slightly from 1.2 to 0.5 V, indicating that the BaTiO3/PMMA dielectric layer effectively encapsulates the sSWCNTs TFTs from absorbing molecules in the environment. Furthermore, the charge pumping current ICP is measured with a gate voltage pulsed at 100 kHz. The maximum ICP increases from 90 to 140nA, which translates to an increase in the interface trap density from 4.5×1011 to 1.1×1012 cm-2eV-1. The charge pumping measurements at the frequency of 10∼250 kHz show that the increase of ICP induced by radiation is obvious when f&amp;gt;30 kHz but is little when f&amp;lt;30 kHz, which indicates that the radiation induced charge traps locate near sSWCNTs. The BaTiO3/PMMA gate dielectric remains to be a good insulator with a leakage current of less than 60 pA after radiation. Such printed flexible TFTs with the polymer gate dielectric possess similar radiation tolerant compared to convention devices on rigid substrates.

P‐29: Solution‐processed Single‐walled Carbon Nanotube Thin Film Transistors In‐situ Patterned by Inkjet‐printing of Surface Treatment Material

We introduce inkjet printing of Poly‐L‐Lysine (PLL) technique to in‐situ pattern the solution‐processed and directly deposited random networks of single‐walled carbon nanotube (SWCNT). And based on this technique, we successfully implemented 8 × 8 SWCNT thin film transistors (TFTs) array on the Si/SiO2 substrate.

Optoelectronic Properties of Printed Photogating Carbon Nanotube Thin Film Transistors and Their Application for Light-Stimulated Neuromorphic Devices.

Artificial synapses/neurons based on electronic/ionic hybrid devices have attracted wide attention for brain-inspired neuromorphic systems since it is possible to overcome the von Neumann bottleneck of the neuromorphic computing paradigm. Here, we report a novel photoneuromorphic device based on printed photogating single-walled carbon nanotube (SWCNT) thin film transistors (TFTs) using lightly n-doped Si as the gate electrode. The drain currents of the printed SWCNT TFTs can gradually increase to over 3000 times of their starting value after being pulsed with light stimulation, and the electrical signals can maintain for over 10 min. These characteristics are similar to the learning and memory functions of brain-inspired neuromorphic systems. The working mechanism of the light-stimulated neuromorphic devices is investigated and described here in detail. Important synaptic characteristics, such as low-pass filtering characteristics and nonvolatile memory ability, are successfully emulated in the printed light-stimulated artificial synapses. It demonstrates that the printed SWCNT TFT photoneuromorphic devices can act as the nonvolatile memory units and perform photoneuromorphic computing, which exhibits potential for future neuromorphic system applications.

Stable Logic Operation of Fiber-Based Single-Walled Carbon Nanotube Transistor Circuits Toward Thread-Like CMOS Circuitry.

A fiber-based single-walled carbon nanotube (SWCNT) thin-film-transistor (TFT) has been proposed. We designed complementary SWCNT TFT circuit based on SPICE simulations, with device parameters extracted from the fabricated fiber-based SWCNT TFTs, such as threshold voltage, contact resistance, and off-/gate-leakage current. We fabricated the SWCNTs CMOS inverter circuits using the selective passivation and n-doping processes on a fiber substrate. By comparing the simulation and experimental results, we could enhance the circuit’s performance by tuning the threshold voltage between p-type and n-type TFTs, reducing the source/drain contact resistance and off current level, and maintaining a low output capacitance of the TFTs. Importantly, it was found that the voltage gain, output swing range, and frequency response of the fiber-based inverter circuits can be dramatically improved.

All-Printed, Self-Aligned Carbon Nanotube Thin-Film Transistors on Imprinted Plastic Substrates.

We present a self-aligned process for printing thin-film transistors (TFTs) on plastic with single-walled carbon nanotube (SWCNT) networks as the channel material. The SCALE (self-aligned capillarity-assisted lithography for electronics) process combines imprint lithography with inkjet printing. Specifically, inks are jetted into imprinted reservoirs, where they then flow into narrow device cavities due to capillarity. Here, we incorporate a composite high- k gate dielectric and an aligned conducting polymer gate electrode in the SCALE process to enable a smaller areal footprint than prior designs that yields low-voltage SWCNT TFTs with average p-type carrier mobilities of 4 cm2/V·s and ON/OFF current ratios of 104. Our work demonstrates the promising potential of the SCALE process to fabricate SWCNT-based TFTs with favorable I- V characteristics on plastic substrates.

Highly flexible printed carbon nanotube thin film transistors using cross-linked poly(4-vinylphenol) as the gate dielectric and application for photosenstive light-emitting diode circuit

In this work, cross-linked poly(4-vinylphenol) (PVP) was utilized in printed single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) as the gate dielectric layer to achieve low operating voltage, environmental stability and high flexibility. The printed top-gate TFTs on polyethylene terephthalate (PET) substrates exhibited effective mobility up to 8.4 cm2V−1s−1 (based on device capacitances measured at 0.1 Hz), on/off ratio of 106 and subthreshold swing (ss) of 63.8 mV/dec at operation voltage of only 1 V. The printed TFTs exhibited excellent mechanical flexibility and stability under ambient conditions due to the use of cross-linked PVP as dielectric layers. No obvious discrepancies in electrical properties were observed after bending 15000 cycles at the radius of 5 mm. A photosensitive light-emitting diode (LED) circuit was constructed, which was composed of two commercial LEDs and the printed SWCNT TFTs. One LED was mounted on top of the gate electrode, acting as a photon sensor to modulate the gate voltage of TFT. The second LED was connected to the source electrode to act as an illuminating device. The circuit could drive the illuminating LED at Vdd of −0.75 V and Vds = −2 V with lighting intensity varying from 0 to 8.96 μW/cm2.