Film Field-effect Transistors Research Articles

Three-dimensional Modeling of Core-structured Field Effect Transistor

Objective: In our previous publication, a core-structured field effect transistor (CoreFET) device shows field effect transistor (FET) behavior. In this work, we investigated factors such as the thickness of the film and the channel on the conductivity of the device in order to optimize the geometry to provide guidance on the fabrication of the device with the best performance. Methods: This study uses Silvaco ATLAS numerical simulation software to investigate the performance of CoreFET. The effects of the thickness of the dielectric layer, SiO2, and the distance between the drain and source (channel length) on the conductivity of the semi-conductor indium gallium zinc oxide (IGZO) have been studied. The flat FET models with the same parameters were used for comparison. Results: Our simulation results demonstrate a directed correlation between the optimized conductivity of the device and the thickness of the dielectric material, as well as the length of the channel. Enhanced sensitivity is achievable by employing a thinner dielectric layer and a narrower channel. Conclusion: According to the results, the device can achieve better performance by optimizing the thickness of the insulator and the gap distance between drain and source electrodes. The remarkable similarity between them indicates that the FET effect remained largely unaffected by variations in FET shape. This observation suggests a consistent outcome across FETs, reinforcing the notion that CoreFET exhibits comparable results as those of film FETs. This finding significantly broadens the scope of CoreFET applications.

Power and Sensitivity Management of Carbon Nanotube Transistor Glucose Biosensors.

Continuous glucose monitoring (CGM), which is significant for the daily management of diabetes, requires a low-power-consumption sensor system that can track low nanomolar levels of glucose in physiological fluids, such as sweat and tears. However, traditional electrochemical methods are limited to analytes in micromolar to millimolar ranges and entail high power consumption. Carbon nanotube (CNT) film field-effect transistors (FETs) are promising for constructing extremely sensitive biosensors, but their wide applications in CGM are limited by the strong screening effect of physiological fluids and the zero charge of glucose molecules. In this study, we demonstrate a glucose aptamer-modified CNT FET biosensor to realize a highly sensitive CGM system with sub-nW power consumption by applying a suitable gate voltage. A positive gate voltage can enlarge the effective Debye screening length at the double layer to reduce the local ion population nearby and then improve the sensitivity of the FET-based biosensors by 5 times. We construct CNT FET sensors for CGM with a limit of detection of 0.5 fM, a record dynamic range up to 109, and a power consumption down to ∼100 pW. The proposed field-modulated sensing performance scheme is applicable to other aptamer-based FET biosensors for detecting neutral or less charged molecules and opens opportunities to develop facilely modulated, highly sensitive, low-power, and noninvasive CGM systems.

Enhancing Oxygen Sensing Precision Through Gate-Controlled TiO2 Field Effect Transistors Under Ultraviolet Excitation

We report on the fabrication and characterization of a novel oxygen sensor based on a TiO2 thin film field effect transistor (FET) deposited on a silicon substrate with an oxide layer by magnetron sputtering. TiO2 is a n-type semiconductor with a wide band gap, which allows the formation of oxygen vacancies or adsorbed oxygen species on its surface under ambient conditions. These oxygen-related defects act as electron traps that modulate the electrical conductivity of the TiO2 film. Under ultraviolet (UV) irradiation, at 310 nm wavelength, the photogenerated carriers in the TiO2 film are captured by the oxygen defects, resulting in a decrease of the film resistance that depends on the oxygen concentration. We demonstrate that the sensitivity and resolution of the oxygen sensor can be enhanced by applying a positive gate voltage to the FET device. The photocurrent variation per unit of oxygen concentration (ΔIphoto/ΔCPO) increases from 1.08 at VG =0 V to 2.5 at VG= 20 V in the range of 5%–20% oxygen concentration. The gate voltage also extends the controllable range of oxygen defects and photocurrent. Our study provides a new insight into the design and optimization of gas sensors based on TiO2 thin film FETs.

Carbon Nanotube Transistor with Colloidal Quantum Dot Photosensitive Gate for Ultrahigh External Quantum Efficiency Photodetector

PbS colloidal quantum dots (CQDs) are promising building block for developing the next-generation high-performance near-infrared (NIR) photodetector. However, due to the surface ligand isolation and surface defects, PbS CQDs usually suffer from low carrier mobility, which limits further optimization of PbS CQDs-based optoelectronic devices. Here, the combination of PbS CQD photodiode and carbon nanotube (CNT) film field-effect transistor (FET) achieves a transistorized NIR photodetector with a photosensitive gate. The photogenerated electrons are drifted to the dielectric surface by a negative gate electric field and built-in electric field, serving as an equivalent gate voltage to turn on the CNT FET, thus realizing the conversion of optical signals to electrical signals. The photodetector exhibits high performance, with a responsivity and detectivity of 41.9 A/W and 3.04 × 1011 Jones under 950 nm illumination, respectively. More importantly, the photodetector achieves an ultrahigh external quantum efficiency (EQE) of 5470% due to the CNT FET amplification function. Besides, the photodetector demonstrates a versatile photoresponse that allows for regulation of responsivity, detectivity, and EQE over a wide range through gate voltage control. The photodetector shows immense potential in NIR photodetection applications, and the distinctive structure of the optical module and electrical module separation also provides fresh thinking for the research and development of the next generation of optoelectronic devices.

Single-walled carbon nanotubes synthesized by laser ablation from coal for field-effect transistors.

Single-walled carbon nanotubes (SWCNTs) have been attracting extensive attention due to their excellent properties. We have developed a strategy of using coal to synthesize SWCNTs for high performance field-effect transistors (FETs). The high-quality SWCNTs were synthesized by laser ablation using only coal as the carbon source and Co-Ni as the catalyst. We show that coal is a carbon source superior to graphite with higher yield and better selectivity toward SWCNTs with smaller diameters. Without any pre-purification, the as-prepared SWCNTs were directly sorted based on their conductivity and diameter using either aqueous two-phase extraction or organic phase extraction with PCz (poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl]). The semiconducting SWCNTs sorted by one-step PCz extraction were used to fabricate thin film FETs. The transformation of coal into FETs (and further integrated circuits) demonstrates an efficient way of utilizing natural resources and a marvelous example in green carbon technology. Considering its short steps and high feasibility, it presents great potential in future practical applications not limited to electronics.

Subthreshold Schottky-contacted carbon nanotube network film field-effect transistors for ultralow-power electronic applications

Ultralow-power electronics is critical to wearable, portable, and implantable applications where the systems could only have access to very limited electrical power supply or even be self-powered. Here, we report on a type of Schottky barrier (SB) contacted single-walled carbon nanotube (SWCNT) network film field-effect-transistors (FETs) that are operated in the subthreshold region to achieve ultralow-power applications. The thin high-k gate dielectric and the overlap between the gate and the source electrodes offer highly efficient gate electrostatic control over the SWCNT channel and the SB at the source contact, resulting in steep subthreshold switching characteristics with a small subthreshold swing (∼67 mV dec−1), a large current on/off ratio (∼106), and a low off-state current (∼0.5 pA). A p-channel metal-oxide-semiconductor inverter built with the subthreshold SB-SWCNT-FETs exhibits a well-defined logic functionality and small-signal amplification capability under a low supply voltage (∼0.5 V) and an ultralow power (∼0.05 pW μm−1). The low-voltage and deep subthreshold operations reported here could lay an essential foundation for high-performance and ultralow-power SWCNTs-based electronics.

Carbon Nanotube Based Radio Frequency Transistors for K-Band Amplifiers.

Owing to the combination of high carrier mobility and saturation velocity, low intrinsic capacitance, and excellent stability, the carbon nanotube (CNT) has been considered as a perfect semiconductor to construct radio frequency (RF) field-effect transistors (FETs) and circuits with an ultrahigh frequency band. However, the reported CNT RF FETs usually exhibited poor real performance indicated by the as-measured maximum oscillation frequency (fmax), and then the amplifiers, which are the most important and fundamental RF circuits, suffered from a low power gain and a low frequency band. In this work, we build RF transistors on solution-derived randomly orientated CNT films with improved quality and uniformity. The randomly orientated CNT film FETs exhibit the record as-measured maximum fmax of 90 GHz, demonstrating the potential for over 28 GHz (at least one-third of 90 GHz) 5G mmWave (frequency range 2) applications. Benefiting from the large-scale uniformity of CNT films, FETs are designed and fabricated with a large channel width to present low internal resistance for the standard 50 Ω impedance matching guide line, which is critical to construct an RF amplifier. Furthermore, we first demonstrate amplifiers with a maximum power gain up to 11 dB and output third-order intercept point (OIP3) of 15 dBm, both at the K-band, which represents the record of a CNT amplifier and is even comparable with a commercial amplifier based on III-V RF transistors.

Highly Temperature‐Stable Carbon Nanotube Transistors and Gigahertz Integrated Circuits for Cryogenic Electronics

AbstractCryogenic electronics are attracting more and more attentions owing to the rising of space exploration and quantum computing, in which low‐temperature stable operation is even more concerned than performance of the integrated circuits (ICs). As a promising semiconducting material, carbon nanotube (CNT) has been extensively explored on its low‐temperature transport characteristics, but the cryogenic electronics application of CNT transistors and ICs has seldom been demonstrated. In this work, the low‐temperature operation of field‐effect transistors (FETs) and ICs built on solution‐derived high semiconducting purity randomly oriented CNT film is investigated. The randomly oriented CNT FETs exhibit much higher temperature stability than the individual CNT based FETs and Si transistors from room temperature to liquid nitrogen temperature, and then the ICs constructed by the CNT film FETs present excellent temperature‐stability. Specifically, the fabricated five‐stage ring oscillators (ROs) exhibit oscillation frequency up to 1.5 GHz with the performance change less than 0.5% at the temperature ranging from 300 to 80 K. The work reveals the great potential of high‐performance transistors and ICs built on randomly oriented CNT films in cryogenic electronics applications.

Homogeneous dual-gate MoS2 field-effect transistors integrated by atomic layer deposition-based film synthesis

Various synthetic approaches have been proposed and studied to grow high-quality two-dimensional (2D) transition metal dichalcogenides (TMDCs) thin films. However, most of current methods suffer from intrinsic material defects or technical limitations. Here, in this paper, large-area few-layer MoS2 thin films have been prepared on SiO2/Si substrate through sulfurizing pre-deposited MoO3 film by atomic layer deposition (ALD). Good film uniformity, crystallinity and stoichiometry have been successfully achieved. The film thickness can be precisely controlled by adjusting the ALD cycle numbers during MoO3 deposition. Field-effect transistor (FET) arrays have been further fabricated based on the large-area MoS2 film. Both back-gate and top-gate geometries have been applied and have shown excellent reproducibility in electrical performance with average electron mobility of 1.71 cm2 V−1 s−1 and 0.31 cm2 V−1 s−1 for the back-gate and top-gate FETs, respectively. Our results have enabled a promising pathway with such thickness-controlled TMD film and homogeneous FET devices towards future low-dimensional nanoelectronics applications.

Changing the Blood Test: Accurate Determination of Mercury(II) in One Microliter of Blood Using Oriented ZnO Nanobelt Array Film Solution-Gated Transistor Chips.

The measurement of ultralow concentrations of heavy metal ions (HMIs) in blood is challenging. A new strategy for the determination of mercury ions (Hg2+ ) based on an oriented ZnO nanobelt (ZnO-NB) film solution-gated field-effect transistor (FET) chip is adopted. The FET chips are fabricated with ZnO-NB film channels with different orientations utilizing the Langmuir-Blodgett (L-B) assembly technique. The combined simulation and I-V behavior results show that the nanodevice with ZnO-NBs parallel to the channel has exceptional performance. The sensing capability of the oriented ZnO-NB film FET chips corresponds to an ultralow minimum detectable level (MDL) of 100 × 10-12 m in deionized water due to the change in the electrical double layer (EDL) arising from the synergism of the field-induced effect and the specific binding of Hg2+ to the thiol groups (-SH) on the film surface. Moreover, the prepared FET chips present excellent selectivity toward Hg2+ , excellent repeatability, and a rapid response time (less than 1 s) for various Hg2+ concentrations. The sensing performance corresponds to a low MDL of 10 × 10-9 m in real samples of a drop of blood.

Speeding up carbon nanotube integrated circuits through three-dimensional architecture

Semiconducting carbon nanotube (CNT) field effect transistor (FET) is attractive for constructing three-dimensional (3D) integrated circuits (ICs) because of its low-temperature processes and low power dissipation. However, CNT based 3D ICs reported usually suffered from lower performance than that of monolayer CNT ICs. In this work, we develop a 3D IC technology through integrating multi-layer high performance CNT film FETs into one chip, and show that it promotes the operation speed of CNT based 3D ICs considerably. We also explore the advantage on ICs of 3D architecture, which brings 38% improvement on speed over two-dimensional (2D) one. Specially, we demonstrate the fabrication of 3D five-stage ring-oscillator circuits with an oscillation frequency of up to 680 MHz and stage delay of 0.15 ns, which represents the highest speed of 3D CNT-based ICs.

Metallic supercurrent field-effect transistor.

In their original formulation of superconductivity, the London brothers predicted1 the exponential suppression of an electrostatic field inside a superconductor over the so-called London penetration depth2-4, λL. Despite a few experiments indicating hints of perturbation induced by electrostatic fields5-7, no clue has been provided so far on the possibility to manipulate metallic superconductors via the field effect. Here, we report field-effect control of the supercurrent in all-metallic transistors made of different Bardeen-Cooper-Schrieffer superconducting thin films. At low temperature, our field-effect transistors show a monotonic decay of the critical current under increasing electrostatic field up to total quenching for gate voltage values as large as ±40 V in titanium-based devices. This bipolar field effect persists up to ~85% of the critical temperature (~0.41 K), and in the presence of sizable magnetic fields. A similar behaviour is observed in aluminium thin-film field-effect transistors. A phenomenological theory accounts for our observations, and points towards the interpretation in terms of an electric-field-induced perturbation propagating inside the superconducting film. In our understanding, this affects the pairing potential and quenches the supercurrent. These results could represent a groundbreaking asset for the realization of all-metallic superconducting field-effect electronics and leading-edge quantum information architectures8,9.

Facile and low-cost mechanical techniques for the fabrication of solution-processed polymer and perovskite thin film transistors

Low-temperature solution-processed polymer and perovskite thin film field effect transistors (FETs) are attractive, as they are compatible with flexible and printed electronics. Given that chemical treatment of the FET channel is expensive and tedious, and sometimes damages the underneath (dielectric) solution-processed layers, in this work, two facile and scalable mechanical treatment techniques are proposed. In the case of polymer FET, the wet spun film was excited by ultrasonic vibration imposed on the substrate. It is demonstrated that the micromixing effect induced by the ultrasonic radiation results in disentanglement, reorganization, and recrystallization of the polymer chains in the wet film. Ultrasonic vibration also improves the film leveling and uniformity and enhances the charge mobility of the channel of the polymer FET. In the case of the perovskite FET, we found that nitrogen blowing over the spun sample of the perovskite solution is a facile, yet effective substitution for the conventional anti-solvent treatment, commonly used to control the solvent evaporation rate. By nitrogen blowing, we achieved a uniform film of perovskite deposited on a solution-processed dielectric layer with domain sizes up to several hundreds of nanometers. By applying these techniques, the linear charge mobility of 0.041 cm2 Vs−1 and 0.055 cm2 Vs−1 were obtained for polymer and perovskite FETs under illumination, respectively. It is shown that while the performance of the polymer FET is only slightly sensitive to illumination, the perovskite FET performs well only under illumination.

Modification of Side Chains of Conjugated Molecules and Polymers for Charge Mobility Enhancement and Sensing Functionality.

Organic semiconductors have received increasing attentions in recent years because of their promising applications in various optoelectronic devices. The key performance metric for organic semiconductors is charge carrier mobility, which is governed by the electronic structures of conjugated backbones and intermolecular/interchain π-π interactions and packing in both microscopic and macroscopic levels. For this reason, more efforts have been paid to the design and synthesis of conjugated frameworks for organic semiconductors with high charge mobilities. However, recent studies manifest that appropriate modifications of side chains that are linked to conjugated frameworks can improve the intermolecular/interchain packing order and boost charge mobilities. In this Account, we discuss our research results in context of modification of side chains in organic semiconductors for charge mobility enhancement. These include the following: (i) The lengths of alkyl chains in sulfur-rich thiepin-fused heteroacences can dramatically influence the intermolecular arrangements and orbital overlaps, ushering in different hole mobilities. Inversely, the lamellar stacking modes of alkyl chains in naphthalene diimide (NDI) derivatives with tetrathiafulvalene (TTF) units are affected by the structures of conjugated cores. (ii) The steric hindrances owing to the bulky branching chains can be weakened by partial replacement of the branching alkyl chains with linear ones for diketopyrrolopyrrole (DPP)-based D (donor)-A (acceptor) conjugated polymers. Such modification of side chains makes the polymer backbones more planar and thus interchain packing order and charge mobilities are improved. The incorporation of hydrophilic tri(ethylene glycol) (TEG) chains into the polymers also leads to improved interchain packing order. In particular, the polymer in which TEG side chains are distributed uniformly exhibits relatively high charge mobility without thermal annealing. (iii) The incorporation of urea groups in the side chains induces the polymer chains to pack more orderly and form large domains because of the additional H-bonding among urea groups. Accordingly, thin film mobilities of the conjugated D-A polymers with side chains entailing urea groups are largely boosted in comparison with those of polymers of the same backbones with either branching alkyl chains or branching/linear alkyl chains. (iv) The torsions of branching alkyl chains in conjugated D-A polymers can be inhibited to some extent upon incorporation of tiny amount of NMe4I in the thin film. As a result, the polymer thin films with NMe4I exhibit improved crystallinity, and charge mobilities can be boosted by more than 20 times. (v) Side chains with functional groups in the conjugated polymers can endow the thin film field-effect transistors (FETs) with sensing functionality. FETs with the conjugated polymer with -COOH groups in the side chains show sensitive, selective, and fast responses toward ammonia and amines, while FETs with the ultrathin films of the polymer containing tetra(ethylene glycol) (TEEG) in the side chains can sense alcohol vapors (in particular ethanol vapor) sensitively and selectively with fast response.

Improving subthreshold swing to thermionic emission limit in carbon nanotube network film-based field-effect

In this letter, we explore the vertical scaling-down behavior of carbon nanotube (CNT) network film field-effect transistors (FETs) and show that by using a high-efficiency gate insulator, we can substantially improve the subthreshold swing (SS) and its uniformity. By using an HfO2 layer with a thickness of 7.3 nm as the gate insulator, we fabricated CNT network film FETs with a long channel (>2 μm) that exhibit an SS of approximately 60 mV/dec. The preferred thickness of HfO2 as the gate insulator in a CNT network FET is between 7 nm and 10 nm, simultaneously yielding an excellent SS (<80 mV/decade) and low gate leakage. However, because of the statistical fluctuations of the network CNT channel, the lateral scaling of CNT network film-based FETs is more difficult than that of conventional FETs. Experiments suggest that excellent SS is difficult to achieve statistically in CNT network film FETs with a small channel length (smaller than the mean length of the CNTs), which eventually limits the further scaling down of this kind of CNT FET to the sub-micrometer regime.

Diketopyrrolopyrrole‐Based Semiconducting Polymer with Both Hydrophobic Alkyl and Hydrophilic Tetraethylene Glycol Chains for Monolayer Transistor and Sensing Application

AbstractFunctional field‐effect transistors (FETs) have received increasing attention in recent years. Herein, it is demonstrated that the incorporation of hydrophilic tetraethylene glycol (TEEG) chains into the diketopyrrolopyrrole (DPP)‐based semiconducting polymer (PDPP3T1) can facilitate the formation of polymeric monolayer at the air–water interface, and the resulting field‐effect transistors (FETs) show sensitive and selective response toward alcohol vapor. By using the Langmuir–Schaefer method, monolayer and ultrathin films from bilayer to five‐layer can be successfully prepared. Interestingly, nanopores with sizes of 50–100 nm are formed within the monolayer film, as observed by using atomic force microscopy. The monolayer FET exhibits relatively high hole mobilities up to 0.014 cm2 V−1 s−1, which is among the highest charge mobilities reported for ultrathin film FETs prepared with the Langmuir technique. Moreover, hole mobility increases with an increase in the thickness of the ultrathin film from monolayer to three‐layer, and it reaches 0.04 cm2 V−1 s−1 for three‐layer FETs. A variation of both on‐current and off‐current is detected for monolayer FET upon exposure to alcohol vapor. The monolayer FET displays ultrahigh sensitivity (down to 1 ppb) and good selectivity toward alcohol vapors, in particular ethanol vapor. This can be attributed to the synergetic effects of the hydrophilic TEEG chains in PDPP3T1 and the nanopores within the monolayers.

Synthesis and characterization of carbazolo[2,1-a]carbazole in thin film and single crystal field-effect transistors

Carbazole-based azaphenacene with high performance in organic field-effect transistors.

Carbon Nanotube Array Field Effect Transistors with High Current Density and On/Off Ratio

Single walled carbon nanotubes (SWCNTs) exhibit extraordinarily high current carrying capacity and suitable band gaps for logic and thin film field-effect transistors (FETs). Progress in honing the exceptional properties of SWCNTs at the multi-tube level, however, has been dampened by incremental advances in the materials science of electronic type sorting and assembly of SWCNTs. To address these challenges we leveraged the exceptional semiconducting sorting fidelity of polyfluorene polymers and we pioneered an alignment technique known as Floating Evaporative Self-Assembly (FESA).1 Recently, we demonstrated individually placed and uniformly pitched purely semiconducting SWCNT arrays using these techniques, allowing for negligible current lost to scaling when the arrays were implemented as the channel in FETs. The SWCNT array FETs exhibited the highest on-state conductance of 261 μS/μm with a simultaneous on/off conductance ratio exceeding 105 for a multi-tube SWCNT FET.2 Here we present our recent optimization of the contact resistance at the palladium-SWCNT interface, which enables a substantial increase in device on-current density compared to our previous report. For SWCNTs, the quality of the contact-semiconductor interface is highly dependent on the SWCNT packing density, film cleanliness, and surface energy, where any non-idealities may lead to poor palladium film adhesion, or even complete film delamination.3 To address the contact challenge we perform surface treatments on the SWCNT array prior to depositing palladium contacts, which involves rinsing the SWCNT arrays in specific solvents and annealing the films in vacuum. In XPS and optical absorbance spectra, we observe significant mass reduction of the polyfluorene wrapper while maintaining the quality and alignment of the SWCNT array. AFM height maps of the palladium contacts deposited on top of the surface treated SWCNTs demonstrate nearly ideal conformation of the palladium on the SWCNT array. The surface-treated SWCNT array FETs exhibit more than 10-fold improvement in the device on-conductance compared to non-treated samples. [1] Y. Joo, G. J. Brady, M. S. Arnold, and P. Gopalan, Langmuir 30 (12), 3460 (2014). [2] G. J. Brady, Y. Joo, M. Y. Wu, M. J. Shea, P. Gopalan, and M. S. Arnold, ACS Nano 8 (11), 11614 (2014). [3] V. Perebeinos and J. Tersoff, Physical Review Letters 114 (8), 4 (2015).

Selectable Synthesis of 2-D MoS2and Its Electronic Devices: From Isolated Triangular Islands to Large-Area Continuous Thin Film

We report on the controllable and selectable synthesis of two-dimensional (2-D) molybdenum disulfide (MoS2 ) by molybdenum trioxide sulfurization with chemical vapor deposition. By controlling the sulfurization timing and substrates positions, the selectable growth of MoS2 isolated triangular islands and continuous thin film was successfully performed independently with the same home-built furnace setup. Also, we found that the hydrofluoric acid substrate treatment took effects on MoS2 nucleation seed densities and modulated the sizes of the triangular islands. Atomic force microscopy and Raman and photoluminescence spectroscopy were used to characterize and compare the properties of MoS2 triangular islands and continuous thin film. The MoS2 triangular islands were monolayers and highly crystalline in nature; where the continuous thin film was formed by small grain size MoS2 nanosheets with smooth surface morphology and a large covered area of up to centimeters. Back-gated field effect transistors (FETs) of as-grown MoS2 triangular islands and continuous thin film were fabricated to analyze their electrical properties. The electron mobilities were measured to be 11.42 and 4.04 cm2/V·s respectively, and with an excellent on/off current ratio up to over 10 8, which demonstrated the good quality of the as-grown MoS2 samples. Furthermore, both the MoS2 triangular islands and continuous thin film FETs exhibited a near ideal current saturation characteristic, which shows the real potential of future applications for 2-D electronic devices.

High Performance Field-Effect Transistors Via Aligned Polyfluorene-Sorted Single-Walled Carbon Nanotube Arrays

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are promising materials for charge transport in field-effect transistor (FET) devices. In order to develop short channel s-SWCNT FETs with high on/off ratios relevant for logic applications, ultra-pure s-SWCNTs of 99.99999% semiconducting purity and higher are needed. There have been many recent studies on the sorting of carbon nanotubes, but most reports have only reached semiconducting purity levels near 99%. In addition, aligned arrays of s-SWCNTs have the potential to improve the mobility and current output of FETs. However, unacceptable semiconducting purity levels (~99%), inter-nanotube charge screening, and inter-nanotube bundling have limited the optimization of such technologies in the short channel regime.1,2 Polyfluorene polymers have been shown to selectively wrap s-SWCNTs on the basis of electronic type, chirality, and diameter. Here we assess the purity and electronic transport properties of aligned arrays of polyfluorene-sorted s-SWCNTs in FET devices. We obtained high purity s-SWCNTs by dispersing nanotube powder in solutions of poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6’-{2,2’-bipyridine)] (PFO-BPy) in toluene following procedures similar to Mistry et al.3 We fabricated well-aligned s-SWCNT arrays by dispersing droplets of of s-SWCNTs at an air water interface, leading to diffusion and self-assembly of nanotubes into well-aligned “stripes” spanning the entire substrate. Finally, we implemented the aligned films as the channel material in field-effect transistors at varying channel lengths ranging from 9 μm to 300 nm. We characterized the films using Raman spectroscopy, AFM and SEM, and found a high degree of alignment, monolayer thickness, and packing density of 50 tubes/micrometer. Previous works on aligned nanotube FETs have used nanotube densities of 200 tubes/micrometer; however, the proximity of nanotubes in these films cause inter-nanotube screening effects resulting lower conductance and mobility values than expected.1 The polyfluorene polymer plays an important role in isolating s-SWCNTs by preventing direct contact, preventing inter-nanotube screening effects.4 The electronic properties of the aligned film FETs were measured demonstrating high values of on/off ratio, mobility, and conductance. In previous studies, device on/off ratios degraded substantially to less than 103 at channel lengths shorter than 1 micrometer, indicating the presence of metallic nanotubes.5 Here we observe a different trend; as the channel length decreases from 9 μm to 300 nm the on/off ratio only decreases from 3x107 to 2x105. This data suggests that m-SWCNTs are far scarcer in our films than in other short channel s-SWCNT FET devices. We estimated purity by counting the number of nanotubes per channel in direct transport regime devices that have channel lengths of 500 nm and shorter. In fact, of the devices measured, encompassing approximately 1,000 nanotubes, zero exhibited metallic character (defined as having an on/off ratio of at least 103), suggesting a s-SWCNT purity of greater than 99.9%.We achieved consistently high performance devices indicated by high mobility in devices that also have high on/off ratios. The highest mobility was 45 cm2/Vs for a 2 μm channel length device with on/off ratio 2x105. We observed high mobility values ranging from 16-45 cm2/Vs across a range of channel lengths. Previous works were limited by purity, leading to trade offs between high on/off ratio and mobility, especially in the direct transport regime.5 Here we demonstrate a route to achieve both a large on/off ratio and high mobility, which is particularly significant for short channel devices in which nanotubes directly span the channel.References 1 Q. Cao, et al., Nature Nanotechnology 8 (3), 180 (2013). 2 M. Engel, et al., ACS Nano 2 (12), 2445 (2008). 3 K S. Mistry, et. al., ACS Nano 7 (3), 2231 (2013). 4 F. Léonard, Nanotechnology 17 (9), 2381 (2006). 5 Nima Rouhi, et al., ACSNANO 5 (11), 8471 (2011).