Single-walled Carbon Nanotube Field-effect Transistors Research Articles

Electrical hysteresis of single-walled carbon nanotube field effect transistors and its modulation by an external magnetic field

Electrical hysteresis in single-walled carbon nanotube (SWNT) field-effect transistors has been observed in 2002, which is a key factor to determine the performance of carbon nanotube field-effect transistors and related systems. Meanwhile, the mechanisms of the hysteresis are controversial and in-depth understanding is still required. In this work, we report the observation of hysteresis in a three-terminal SWNT FET at room temperature under atmospheric conditions. The hysteresis is found to be modulated by an external magnetic field. And there is a significant difference for the modulation of the hysteresis between the positive and negative magnetic fields. Possible mechanism is proposed and discussed.

Analytical Prediction of Highly Sensitive CNT-FET-Based Sensor Performance for Detection of Gas Molecules

In this study, a set of new analytical models to predict and investigate the impacts of gas adsorption on the electronic band structure and electrical transport properties of the single-wall carbon nanotube field-effect transistor (SWCNT-FET) based gas sensor are proposed. The sensing mechanism is based on introducing new hopping energy and on-site energy parameters for gas-carbon interactions representing the charge transfer between gas molecules (CO2, NH3, and H2O) and the hopping energies between carbon atoms of the CNT and gas molecule. The modeling starts from the atomic level to the device level using the tight-binding technique to formulate molecular adsorption effects on the energy band structure, density of states, carrier velocity, and I-V characteristics. Therefore, the variation of the energy bandgap, density of states and current-voltage properties of the CNT sensor in the presence of the gas molecules is discovered and discussed. The simulated results show that the proposed analytical models can be used with an electrical CNT gas sensor to predict the behavior of sensing mechanisms in gas sensors.

Ultra-sensitive NO2 gas sensors based on single-wall carbon nanotube field effect transistors: Monitoring from ppm to ppb level

Owing to their sensitive chemical-to-electrical transducer capabilities and compatibility with device miniaturization and low operation temperature, single-walled carbon nanotube field-effect transistor (SWCNT-FET) represents an attractive platform to provide solutions in the gas sensing field. In this work, SWCNT-FETs were fabricated and their performances for detecting low NO2 concentrations were evaluated. Outstanding devices response was obtained, which was shown to follow a 2 power law dependence between the response and the NO2 concentration in the range of 100 ppb up to 10 ppm. Such ultra-high response is attributed to an enhancement of the Schottky barrier modulation triggered by the specific device configuration. The device configuration is based on individual semiconducting SWCNTs directly connecting the interdigitated Source-Drain electrodes. To the best of our knowledge, the results reported here correspond to the most sensitive device among the devices based on non-functionalized carbon materials and operational at low temperatures. Furthermore, the obtained results are supported by a deep SWCNT characterization, and the changes in Schottky barrier's height induced by the presence of gas molecules are estimated and discussed. Overall, the present reported results provide useful information for establishing a robust process for the fabrication of the next generation of CNT based gas-sensing devices.

Improved Electron Injection and Transport in Semiconducting Polymers By Doping with Guanidino-Functionalized Aromatic Compounds

Efficient and stable n-dopants are still rare but highly desired for organic electronics and thermoelectrics. Many high mobility, n-type semiconducting polymers still show some hole transport, which is unwanted for applications in complementary inverters, as it gives rise to increased power dissipation. The use of n-type contact dopants that block the injection of holes is thus beneficial. We successfully applied 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb), a guanidino-functionalized aromatic (GFA) compound, as a strong two-electron donor to networks of single-walled carbon nanotube field-effect transistors to create purely n-type devices with high electron mobilities and high on/off current ratios [1]. Here, we demonstrate the versatility of this dopant by applying it to the well-known n-type (but still slightly ambipolar) polymer semiconductor P(NDI2OD-T2).The dopant ttmgb can be processed directly from solution, which leads to significantly improved device characteristics. Additionally, we show that vapor deposition of ttmgb is another pathway to high-performance injection layers. In all cases, the injection of electrons and their mobility is significantly improved compared to the untreated reference samples. In addition, the injection of holes is blocked by ttmgb2+ on the electrode surface, which enables the fabrication of solely n-type FETs. Contact doping with ttmgb and other GFAs could potentially also be used on other semiconducting materials, e.g. for two-dimensional transition metal dichalcogenides, and may find widespread application in high performance thin film electronics. [1] Schneider et al., ACS Nano 2018, 12 (6), 5895-5902 Figure 1

Probing Ca2+-induced conformational change of calmodulin with gold nanoparticle-decorated single-walled carbon nanotube field-effect transistors.

Nanomaterials are ideal for electrochemical biosensors, with their nanoscale dimensions enabling the sensitive probing of biomolecular interactions. In this study, we compare field-effect transistors (FET) comprised of unsorted (un-) and semiconducting-enriched (sc-) single-walled carbon nanotubes (SWCNTs). un-SWCNTs have both metallic and semiconducting SWCNTs in the ensemble, while sc-SWCNTs have a >99.9% purity of semiconducting nanotubes. Both SWCNT FET devices were decorated with gold nanoparticles (AuNPs) and were then employed in investigating the Ca2+-induced conformational change of calmodulin (CaM) - a vital process in calcium signal transduction in the human body. Different biosensing behavior was observed from FET characteristics of the two types of SWCNTs, with sc-SWCNT FET devices displaying better sensing performance with a dynamic range from 10-15 M to 10-13 M Ca2+, and a lower limit of detection at 10-15 M Ca2+.

Affinity sensor for haemoglobin A1c based on single-walled carbon nanotube field-effect transistor and fructosyl amino acid binding protein

Haemoglobin A1c (HbA1c) is a significant glycaemic marker for diabetes mellitus. The level of HbA1c reflects the mean blood glucose level over the prior 2–3 months and it is useful for the assessment of therapeutic effectiveness and for diagnosis. In this study, we report the label-free affinity sensor for HbA1c based on the chemiresistor-type field-effect transistor, which has a simple sensor configuration. Single-walled carbon nanotubes (SWNTs) were used as the transducing element. The fructosyl amino acid binding protein from Rhizobium radiobacter (SocA), which binds to α-fructosyl amino acid specifically, was used as the biorecognition element for fructosyl valine (FV), the product of the proteolytic hydrolysis of HbA1c. The developed sensor shows the ability to measure as low as 1.2 nM FV, which is 14-fold more sensitive compared to the previously reported fluorescence-based sensor using SocA. This sensor also exhibits high specificity where no significant response is observed from either fructosyl lysine (FK) or glucose, which are potential interferents. FK is the ε-fructosyl amino acid from glycated albumin, another glycated protein, whereas glucose is naturally present at very high concentration in the blood. We propose that the modulation of the surface charges on the SWNTs caused by the conformational change in SocA upon ligand binding leads to the proportionate changes in the number of carriers in the SWNT channel.

Oligomer Hydrate Crystallization Improves Carbon Nanotube Memory

Single-walled carbon nanotube (SWCNT) field-effect transistor (FET) devices have potential for memory storage applications. Devices fabricated with semiconducting SWCNT ink using dielectrophoresis were coated with a renewably sourced poly(oxacyclobutane) oligomer. It was found that this oligomer crystallizes with water to form a semicrystalline oligomer hydrate material. Crystallization also occurs on the SWCNT device surface in ambient conditions, resulting in dramatically increased hysteresis of the SWCNT-FET I-Vg curves. Using alternating current impedance measurements, we found that the oligomer hydrate crystals store charge, acting as a capacitor encapsulating the nanotube network. This capacitive material can serve to electrostatically gate the SWCNT network. The charge storage properties of the oligomer hydrate crystals were applied to store “0” and “1” bits separated by ∼4 orders of magnitude of current. Utilizing powder X-ray diffraction and simulation, we have demonstrated that this semicrystall...

Label-Free Biosensor Using a Silver Specific RNA-Cleaving DNAzyme Functionalized Single-Walled Carbon Nanotube for Silver Ion Determination.

Silver, a very common heavy metal, has been employed in electronics, medicine, jewelry, and catalysis due to its excellent chemical and physical characteristics. Silver-containing wastes can cause environmental pollution, so it is vital to monitor the Ag(I) concentration. Here, a label-free biosensor was developed for the Ag(I) detection, which used single-walled carbon nanotubes/field effect transistor (SWNTs/FET) to functionalize with a specific DNAzyme, containing an Agzyme and a complementary strand DNA (CS-DNA) embedded an RNA-base. The CS-DNA was covalently immobilized on the SWNTs’ surface through peptide bonds, and then combined with the Agzyme. When Ag(I) was bound with the Agzyme, the CS-DNA can be cleaved at the RNA site efficiently. The cleaved DNAzyme induced a remarkable change in the electrical conductivity of SWNTs. The performances of DNAzyme/SWNTs/FET were investigated using different spectroscopy and electrochemical methods. Under the optimized parameters, DNAzyme/SWNTs/FET presented a high sensitivity and selectivity towards Ag(I), in which the linear response range is 10 pM to 106 pM and the limit of detection is 5 pM(S/N = 3). Additionally, the prepared biosensor was applied to measure the Ag(I) concentration in the water sample with good results.

On/off ratio enhancement in single-walled carbon nanotube field-effect transistor by controlling network density via sonication

Single-walled carbon nanotube (SWCNT) is generally used as a networked structure in the fabrication of a field-effect transistor (FET) since it is known that one-third of SWCNT is electrically metallic and the remains are semiconducting. In this case, the presence of metallic paths by metallic SWCNT (m-SWCNT) becomes a significant technical barrier which hinders the networks from achieving a semiconducting behavior, resulting in a low on/off ratio. Here, we report on an easy method of controlling the on/off ratio of a FET where semiconducting SWCNT (s-SWCNT) and m-SWCNT constitute networks between source and drain electrodes. A FET with SWCNT networks was simply sonicated under water to control the on/off ratio and network density. As a result, the FET having an almost metallic behavior due to the metallic paths by m-SWCNT exhibited a p-type semiconducting behavior. The on/off ratio ranged from 1 to 9.0 × 104 along sonication time. In addition, theoretical calculations based on Monte-Carlo method and circuit simulation were performed to understand and explain the phenomenon of a change in the on/off ratio and network density by sonication. On the basis of experimental and theoretical results, we found that metallic paths contributed to a high off-state current which leads to a low on/off ratio and that sonication formed sparse SWCNT networks where metallic paths of m-SWCNT were removed, resulting in a high on/off ratio. This method can open a chance to save the device which has been considered as a failed one due to a metallic behavior by a high network density leading to a low on/off ratio.

Peptide aptamer-modified single-walled carbon nanotube-based transistors for high-performance biosensors

Biosensors employing single-walled carbon nanotube field-effect transistors (SWCNT FETs) offer ultimate sensitivity. However, besides the sensitivity, a high selectivity is critically important to distinguish the true signal from interference signals in a non-controlled environment. This work presents the first demonstration of the successful integration of a novel peptide aptamer with a liquid-gated SWCNT FET to achieve highly sensitive and specific detection of Cathepsin E (CatE), a useful prognostic biomarker for cancer diagnosis. Novel peptide aptamers that specifically recognize CatE are engineered by systemic in vitro evolution. The SWCNTs were firstly grown using the thermal chemical vapor deposition (CVD) method and then were employed as a channel to fabricate a SWCNT FET device. Next, the SWCNTs were functionalized by noncovalent immobilization of the peptide aptamer using 1-pyrenebutanoic acid succinimidyl ester (PBASE) linker. The resulting FET sensors exhibited a high selectivity (no response to bovine serum albumin and cathepsin K) and label-free detection of CatE at unprecedentedly low concentrations in both phosphate-buffered saline (2.3 pM) and human serum (0.23 nM). Our results highlight the use of peptide aptamer-modified SWCNT FET sensors as a promising platform for near-patient testing and point-of-care testing applications.

Solution-processed polymer-sorted semiconducting carbon nanotube network transistors with low-k /high-k bilayer polymer dielectrics

Solution-processed semiconducting carbon nanotube transistors with a high mobility and an ON/OFF ratio are the most promising for use in flexible electronics. In this paper, we report low-k/high-k bilayer polymer dielectrics for solution-processed semiconducting single-walled carbon nanotube (s-SWNT) field-effect transistors (s-SWNT-FETs) with efficient charge transport and operation at low voltage. Thin low-k polystyrene (10 nm) is used for the first contact insulator with a channel in order to passivate the dipolar disorder induced by high-k insulators. The second gate insulator for low voltage operation is cyanoethyl pullulan (CEP), which is an environmentally friendly high-k insulator based on cellulose. Moreover, poly[(vinylidenefluoride-co-trifluoroethylene) is chosen as a single layer dielectric for comparison. A reasonably low operational voltage (<10 V) and high operational stability are achieved by the s-SWNT-FETs with polystyrene/CEP bilayer gate dielectrics. In addition, this indicates that the interface between the s-SWNTs and the low-k insulator is of critical importance for efficient charge transport.

A simple and real-time sensing of human serum albumin using antibody-modified CNT-FET

Microalbuminuria is a key indicator for the treatment of cardiovascular or cerebrovascular diseases and death. Therefore, sensitive and specific detection methods of HSA in biological fluids especially in low concentration are necessary in diagnosis and preventive medicine. Here, nanostructured electrical immunosensor is demonstrated for the rapid, sensitive and selective detection of human serum albumin (HSA), using single-walled carbon nanotube (swCNT) field-effect transistor (FETs) functionalized with monoclonal anti-human serum albumin (mAHSA) via simple coating. The selective binding of HSA with mAHSA on the surface of swCNT induces the electrostatic gating effect to the swCNT-FET. The resulting sensor exhibited high sensitivity toward HSA in real time, with good selectivity. The proposed method provides a powerful platform for a real time, sensitive and selective monitoring of HSA in biological fluids.

High performance dendrimer functionalized single-walled carbon nanotubes field effect transistor biosensor for protein detection

We report a single-walled carbon nanotube (SWNT) field-effect transistor (FET) functionalized with Polyamidoamine (PAMAM) dendrimer with 128 carboxyl groups as anchors for site specific biomolecular immobilization of protein antibody for C-reactive protein (CRP) detection. The FET device was characterized by scanning electron microscopy and current-gate voltage (I-Vg) characteristic studies. A concentration-dependent decrease in the source-drain current was observed in the regime of clinical significance, with a detection limit of ∼85 pM and a high sensitivity of 20% change in current (ΔI/I) per decade CRP concentration, showing SWNT being locally gated by the binding of CRP to antibody (anti-CRP) on the FET device. The low value of the dissociation constant (Kd = 0.31 ± 0.13 μg ml−1) indicated a high affinity of the device towards CRP analyte arising due to high anti-CRP loading with a better probe orientation on the 3-dimensional PAMAM structure.

High On/Off Ratio Field-Effect Transistor Based on Semiconducting Single-Walled Carbon Nanotubes by Selective Separation

A semiconducting single-walled carbon nanotube field-effect transistor (SWCNT FET) was prepared using the simple technique of selective separation. The Raman spectrum of the transistor revealed that the m-SWCNTs and regioregular poly (3-dodecylthiophene) were completely removed, leaving only s-SWCNTs. The drain current–drain voltage (ID–VD) characteristics of an SWCNT FET device in the dark were measured. The transistor exhibited a high on/off ratio with a selective separation of 107 and a subthreshold swing of 154 mV/dec. The effective s-SWCNT sorting process in this study can be applied to more electronic devices in the future.

Effect of Polymer Gate Dielectrics on Charge Transport in Carbon Nanotube Network Transistors: Low-k Insulator for Favorable Active Interface.

Charge transport in carbon nanotube network transistors strongly depends on the properties of the gate dielectric that is in direct contact with the semiconducting carbon nanotubes. In this work, we investigate the dielectric effects on charge transport in polymer-sorted semiconducting single-walled carbon nanotube field-effect transistors (s-SWNT-FETs) by using three different polymer insulators: A low-permittivity (εr) fluoropolymer (CYTOP, εr = 1.8), poly(methyl methacrylate) (PMMA, εr = 3.3), and a high-εr ferroelectric relaxor [P(VDF-TrFE-CTFE), εr = 14.2]. The s-SWNT-FETs with polymer dielectrics show typical ambipolar charge transport with high ON/OFF ratios (up to ∼105) and mobilities (hole mobility up to 6.77 cm2 V-1 s-1 for CYTOP). The s-SWNT-FET with the lowest-k dielectric, CYTOP, exhibits the highest mobility owing to formation of a favorable interface for charge transport, which is confirmed by the lowest activation energies, evaluated by the fluctuation-induced tunneling model (FIT) and the traditional Arrhenius model (EaFIT = 60.2 meV and EaArr = 10 meV). The operational stability of the devices showed a good agreement with the activation energies trend (drain current decay ∼14%, threshold voltage shift ∼0.26 V in p-type regime of CYTOP devices). The poor performance in high-εr devices is accounted for by a large energetic disorder caused by the randomly oriented dipoles in high-k dielectrics. In conclusion, the low-k dielectric forms a favorable interface with s-SWNTs for efficient charge transport in s-SWNT-FETs.

Design and manufacture of TNT explosives detector sensors based on CNTFET

Purpose Miniaturized smart sensors that can perform sensitive and selective real-time monitoring of target analytes are tremendously valuable for various sensing applications. So, the purpose of this paper is to provide details of sensors based on selective nanocoatings by combining trinitrotoluene (TNT) receptors bound to conjugated polydiacetylene (PDA) polymers with single-walled carbon nanotube field-effect transistors (CNTFETs) for detecting explosives TNT. Design/methodology/approach Following an introduction, this paper describes the way of creating an FET with CNTs, which are functionalized by the peptide based on TNT molecule recognition elements and PDA, to offer a system which has the capability of answering the presence of related target molecules (TNT). Finally, brief conclusions are drawn. Findings Single-wall nanotubes and reduced graphene oxide are interesting materials for creating biosensors of FETs at nanoscale because of unique electrical, mechanical, geometrical and biocompatible properties. Therefore, this sensor is designed and manufactured, and the results of applying TNT to sensor show good sensitivity and selectivity response. Originality/value In this timeframe of history, sensors based on CNTFET are required for different uses, including clinical diagnosis technologies, environmental tests and bioterrorism recognition technologies, that correspond to the military conflicts and terrorism. So, CNTFET sensor design provides real-time detection of TNT explosives.

Enhancement of carbon nanotube FET performance via direct synthesis of poly (sodium 4-styrenesulfonate) in the transistor channel

Direct synthesis of poly (sodium 4-styrenesulfonate) (P(NaSS)) inside the channel of single-walled carbon nanotube (SWCNT) field-effect transistors (FETs), is shown to be highly beneficial in improving the device parameters. Starting with monomeric compounds, the FET-channel was in-situ polymerized, using the self-initiated photografting and photopolymerization process. Upon formation of the P(NaSS) polymer matrix, we report improved device-to-device consistency, lower variability in the threshold voltage, higher drain currents and higher on/off ratios. Annealing in vacuum was shown to further improve the device performance and induce an ambipolar behavior. Moreover, those FET devices showed a long-term stability even under ambient environment.

Electron Back Scattering in CNTFETs

A new non-ballistic analytical model for the intrinsic channel region of MOSFET-like single-walled carbon-nanotube field-effect transistors with ohmic contacts has been developed which overcomes the limitations of existing models and extends their applicability toward high bias voltages needed for analog applications. The new model comprises an improved description of electron-phonon scattering mechanism taking into account the accumulation of electrons at the bottom of conduction subband due to back scattering by optical phonons. The model has been justified by a Boltzmann transport equation solver. The simulation results are found to be in agreement with experimental data for highly doped CNTFETs.

Single-Molecule Electronic Measurements of DNA Polymerase I

Single-molecule techniques based on optical, electronic, and mechanical mechanisms have all proven useful for studying enzymes like DNA polymerases. Electronic devices, in particular, provide exciting new opportunities for understanding polymerase activity, especially with regard to improving DNA sequencing technologies. Recently, single molecule kinetics of the Klenow fragment (KF) of polymerase I have been studied by bioconjugating KF to single-walled carbon nanotube field-effect transistors. Continuous recordings of KF processing various DNA templates have extended over 600 seconds and through >10,000 bond-forming events, providing new insights into KF's processivity, kinetic variability, and tolerance of various dNTP analogs (1,2). For example, we show that the average duration of each incorporation event appears invariant across all analog and native dNTPs, indicating that analog structure has no impact on the timing of this step of the catalytic cycle. Despite similar timings, however, polymerization with some analogs have revealed alternate conformational states that do not occur with native dNTPs. The electronic technique's particular sensitivity to allosteric motions implicates a special role for KF's O-helix as it tests the stability of nascent base pairs with these analogs. The results help explain polymerases’ tolerance for dNTP analogs, despite having highly evolved mechanisms for specific recognition of and discrimination among dNTPs.1. T.J. Olsen, et. al., “Electronic Measurements of Single-Molecule Processing by DNA polymerase I (Klenow fragment),” JACS 135, 7855 (2013).2. K.M. Pugliese, et. al., “Processive Incorporation of Deoxynucleoside Triphosphate Analogs by Single-Molecule DNA Polymerase I (Klenow Fragment) Nanocircuits.” JACS 137, 9587 (2015).

Layer-by-Layer Assembled 2D Montmorillonite Dielectrics for Solution-Processed Electronics.

Layer-by-layer assembled 2D montmorillonite nanosheets are shown to be high-performance, solution-processed dielectrics. These scalable and spatially uniform sub-10 nm thick dielectrics yield high areal capacitances of ≈600 nF cm(-2) and low leakage currents down to 6 × 10(-9) A cm(-2) that enable low voltage operation of p-type semiconducting single-walled carbon nanotube and n-type indium gallium zinc oxide field-effect transistors.