Scaling of N-Type Field-Effect Transistors Based on Aligned Carbon Nanotube Arrays

Wafer-scale aligned carbon nanotubes (A-CNTs) are promising candidate semiconductors for building high-performance complementary metal-oxide-semiconductor (CMOS) transistors for future integrated circuits (ICs). A-CNT-based p-type field-effect transistors (P-FETs) have demonstrated excellent performance and scalability down to sub-10 nm nodes. However, the development of A-CNT n-type FETs (N-FETs) lags far behind, in regard to their electronic performance and device scaling. In this work, we fabricated top-gated N-FETs based on A-CNTs with a scandium (Sc)-contacted source and drain. High-performance A-CNT N-FETs were demonstrated with record on-state current (Ion) exceeding 1 mA/μm and peak transconductance (gm) of 0.4 mS/μm. Interestingly, the A-CNT N-FETs exhibited abnormal scaling behavior owing to the lateral oxidation of low-work function source/drain contacts, leading to formidable challenges to scale both the gate length (Lg) and the contact length (Lc) at the same time. Understanding of the abnormal scaling behavior contributes to seeking solutions for high-performance A-CNT N-FETs, and it paves the way for future CNT CMOS digital IC technology.

Reproducible, Accurate, and Sensitive Food Toxin On-Site Detection with Carbon Nanotube Transistor Biosensors

Field-effect transistor (FET) biosensors based on nanomaterials are promising in the areas of food safety and early disease diagnosis due to their ultrahigh sensitivity and rapid response. However, most academically developed FET biosensors lack real-world reproducibility and comprehensive methodological validation to meet the standards of regulatory bodies. Here, highly uniform and well-packaged semiconducting carbon nanotube (CNT) FET biosensor chips were developed and assessed for the plug-and-play sensing for the rapid and highly sensitive detection of aflatoxin B1 (AFB1) in real food samples to meet international standards. In order to meet the requirements for reproducibility and stability, a scalable residual-free passivation and packaging process was developed for CNT FET biosensors. Portable detection systems were then constructed for on-site detection. The resulting packaged chips were functionalized with nucleic aptamers to enable highly selective detection of AFB1 in food samples with a detection limit (LOD) of 0.55 fg/mL (standard) for AFB1 and cross-reactivity coefficients to interferences as low as 1.8 × 10-7 in simulated solutions. Utilizing the portable detection system, on-site real food detection was achieved with a rapid response time less than 60 s, and LOD of 0.25 pg/kg (standard) in complex corn sample matrices. Single-blind tests demonstrated the ability of the chips to detect AFB1-positive food with 100% accuracy, using a set of 30 peanut samples. Validation experiments confirmed that the detection range, stability, and repeatability met international standards. This study showcased the accuracy, reliability, and potential practical applications of CNT FET biosensor chips in areas such as food safety and rapid biomedical testing.

Photoinduced Nonadiabatic Dynamics of a Single-Walled Carbon Nanotube-Porphyrin Complex

Single-walled carbon nanotubes (SWCNTs) have gained a lot of attention in the past few decades due to their promising optoelectronic properties. In addition, SWCNTs can form complexes that have good chemical stability and transport properties with other optical functional materials through noncovalent interactions. Elucidating the detailed mechanism of these complexes is of great significance for improving their optoelectronic properties. Nevertheless, simulating the photoinduced dynamics of these complexes accurately is rather challenging since they usually contain hundreds of atoms. To save computational efforts, most of the previous works have ignored the excitonic effects by employing nonadiabatic carrier (electron and hole) dynamics simulations. To properly consider the influence of excitonic effects on the photoinduced ultrafast processes of the SWCNT-tetraphenyl porphyrin (H2TPP) complex and to further improve the computational efficiency, we developed the nonadiabatic molecular dynamics (NAMD) method based on the extended tight binding-based simplified Tamm-Dancoff approximation (sTDA-xTB), which is applied to study the ultrafast photoinduced dynamics of the noncovalent SWCNT-porphyrin complex. In combination with statically electronic structure calculations, the present work successfully reveals the detailed microscopic mechanism of the ultrafast excitation energy transfer process of the complex. Upon local excitation on the H2TPP molecule, an ultrafast energy transfer process occurs from H2TPP (SWCNT-H2TPP*) to SWCNT (SWCNT*-H2TPP) within 10 fs. Then, two slower processes corresponding to the energy transfer from H2TPP to SWCNT and hole transfer from H2TPP to SWCNT take place in the 1 ps time scale. The sTDA-xTB-based electronic structure calculation and NAMD simulation results not only match the previous experimental observations from static and transient spectra but also provide more insights into the detailed information on the complex's photoinduced dynamics. Therefore, the sTDA-xTB-based NAMD method is a powerful theoretical tool for studying the ultrafast photoinduced dynamics in large extended systems with a large number of electronically excited states, which could be helpful for the subsequent design of SWCNT-based functional materials.

Morphological Evolution of Atomic Layer Deposited Hafnium Oxide on Aligned Carbon Nanotube Arrays

Microscopic study of the nucleation and growth of atomic layer deposition (ALD) dielectrics onto carbon nanotubes (CNTs) is an essential while challenging task toward high-performance devices. Here, we capture the morphological evolution and growth behaviors of ALD-HfO2 onto SiO2/Si-supported aligned CNT arrays (A-CNTs) under three ALD recipes via cross-sectional high-resolution scanning transmission electron microscopy. The HfO2 in ALD I (200 °C) preferentially nucleates on the SiO2 substrate in heterogeneous growth mode, resulting in films with considerable pinholes, while ALD II (90 °C) and III (90 °C and extra H2O presoak) exhibit homogeneous growth with nucleation on both SiO2 and CNTs, yielding uniform films. Arrangement defects in A-CNTs exacerbate nonuniformity of HfO2 and tube-tube separation plays deterministic roles affecting the HfO2-CNT interfacial morphology. Electrical measurements from A-CNTs metaloxide-semiconductor devices validate these findings. Our investigation contributes valuable insights for optimizing ALD processes for enhanced dielectric integration on A-CNTs in next-generation electronics.

Investigation on Junction Contacts of Semiconducting Carbon Nanotube Networks Using Conductive Atomic Force Microscopy

Semiconductor single-walled carbon nanotube (s-SWNT) networks have gained prominence in electronic devices due to their cost-effectiveness, relatively production-naturality, and satisfactory performance. Configuration, density, and resistance of SWNT-SWNT junctions are considered crucial factors influencing the overall conductivity of s-SWNT networks. In this study, we present a method for inferring the lower bounds of the SWNT-SWNT junction resistance in s-SWNT networks based on conductive atomic force microscopy TUNA images. This method further enables the proposal of a classification for SWNT-SWNT junctions based on the current behavior relative to their surroundings. The three types of SWNT-SWNT junctions are denoted as (i) true contact (T), (ii) poor contact (P), and (iii) false contact (F). Of them, the true and poor contacts, respectively, represent good and poor electrical contact for the subject SWNT-SWNT junctions whose electrical conductivity hardly improves under external tip pressure, while that of the false contact can be further improved by external pressure. Statistical analysis demonstrates that while T-type junctions make a significant contribution to network conductivity, their proportion accounts for only approximately 40%. The P-type and F-type junctions, which constitute over 60% of the total, may be a contributing factor that constrains the overall conductivity of the s-SWNT networks. The height ratio of the junction to the sum of two SWNTs was also observed to exhibit variations among the three types. Finally, we propose a three-dimensional model to elucidate the formation mechanism underlying each type of junction. The present study provides insights into the performance of spontaneous contacts between s-SWNTs in the networks, and the systematic image acquisition and junction classification processes may provide support for future advancements in these networks.

Formation, Structure, Electronic, and Transport Properties of Nitrogen Defects in Graphene and Carbon Nanotubes

The substitutional doping of nitrogen is an efficient way to modulate the electronic properties of graphene and carbon nanotubes (CNTs). Therefore, it could enhance their physical and chemical properties as well as offer potential applications. This paper provides an overview of the experimental and theoretical investigations regarding nitrogen-doped graphene and CNTs. The formation of various nitrogen defects in nitrogen-doped graphene and CNTs, which are identified by several observations, is reviewed. The electronic properties and transport characteristics for nitrogen-doped graphene and CNTs are also reviewed for the development of high-performance electronic device applications.

Surface and interfacial sciences for future technologies

Physical science has undergone an evolutional transition in research focus from solid bulks to surfaces, culminating in numerous prominent achievements. Currently, it is experiencing a new exploratory phase-interfacial science. Many a technology with a tremendous impact is closely associated with a functional interface which delineates the boundary between disparate materials or phases, evokes complexities that surpass its pristine comprising surfaces, and thereby unveils a plethora of distinctive properties. Such an interface may generate completely new or significantly enhanced properties. These specific properties are closely related to the interfacial states formed at the interfaces. Therefore, establishing a quantitative relationship between the interfacial states and their functionalities has become a key scientific issue in interfacial science. However, interfacial science also faces several challenges such as invisibility in characterization, inaccuracy in calculation, and difficulty in precise construction. To tackle these challenges, people must develop new strategies for precise detection, accurate computation, and meticulous construction of functional interfaces. Such strategies are anticipated to provide a comprehensive toolbox tailored for future interfacial science explorations and thereby lay a solid scientific foundation for several key future technologies.

Two-Dimensional Semiconductors for State-of-the-Art Complementary Field-Effect Transistors and Integrated Circuits

As the trajectory of transistor scaling defined by Moore's law encounters challenges, the paradigm of ever-evolving integrated circuit technology shifts to explore unconventional materials and architectures to sustain progress. Two-dimensional (2D) semiconductors, characterized by their atomic-scale thickness and exceptional electronic properties, have emerged as a beacon of promise in this quest for the continued advancement of field-effect transistor (FET) technology. The energy-efficient complementary circuit integration necessitates strategic engineering of both n-channel and p-channel 2D FETs to achieve symmetrical high performance. This intricate process mandates the realization of demanding device characteristics, including low contact resistance, precisely controlled doping schemes, high mobility, and seamless incorporation of high- κ dielectrics. Furthermore, the uniform growth of wafer-scale 2D film is imperative to mitigate defect density, minimize device-to-device variation, and establish pristine interfaces within the integrated circuits. This review examines the latest breakthroughs with a focus on the preparation of 2D channel materials and device engineering in advanced FET structures. It also extensively summarizes critical aspects such as the scalability and compatibility of 2D FET devices with existing manufacturing technologies, elucidating the synergistic relationships crucial for realizing efficient and high-performance 2D FETs. These findings extend to potential integrated circuit applications in diverse functionalities.

Mass Production of Carbon Nanotube Transistor Biosensors for Point-of-Care Tests

Low-dimensional semiconductor-based field-effect transistor (FET) biosensors are promising for label-free detection of biotargets while facing challenges in mass fabrication of devices and reliable reading of small signals. Here, we construct a reliable technology for mass production of semiconducting carbon nanotube (CNT) film and FET biosensors. High-uniformity randomly oriented CNT films were prepared through an improved immersion coating technique, and then, CNT FETs were fabricated with coefficient of performance variations within 6% on 4-in. wafers (within 9% interwafer) based on an industrial standard-level process. The CNT FET-based ion sensors demonstrated threshold voltage standard deviations within 5.1 mV at each ion concentration, enabling direct reading of the concentration information based on the drain current. By integrating bioprobes, we achieved detection of biosignals as low as 100 aM through a plug-and-play portable detection system. The reliable technology will contribute to commercial applications of CNT FET biosensors, especially in point-of-care tests.

High-Performance Semiconducting Carbon Nanotube Transistors Using Naphthalene Diimide-Based Polymers with Biaxially Extended Conjugated Side Chains

Polymer-wrapped single-walled carbon nanotubes (SWNTs) are a potential method for obtaining high-purity semiconducting (sc) SWNT solutions. Conjugated polymers (CPs) can selectively sort sc-SWNTs with different chiralities, and the structure of the polymer side chains influences this sorting capability. While extensive research has been conducted on modifying the physical, optical, and electrical properties of CPs through side-chain modifications, the impact of these modifications on the sorting efficiency of sc-SWNTs remains underexplored. This study investigates the introduction of various conjugated side chains into naphthalene diimide-based CPs to create a biaxially extended conjugation pattern. The CP with a branched conjugated side chain (P3) exhibits reduced aggregation, resulting in improved wrapping ability and the formation of larger bundles of high-purity sc-SWNTs. Grazing incidence X-ray diffraction analysis confirms that the potential interaction between sc-SWNTs and CPs occurs through π-π stacking. The field-effect transistor device fabricated with P3/sc-SWNTs demonstrates exceptional performance, with a significantly enhanced hole mobility of 4.72 cm2 V-1 s-1 and high endurance/bias stability. These findings suggest that biaxially extended side-chain modification is a promising strategy for improving the sorting efficiency and performance of sc-SWNTs by using CPs. This achievement can facilitate the development of more efficient and stable electronic devices.

Achieving High-Performance Polymer-Wrapper-Free Aligned Carbon Nanotube Field-Effect Transistors Through Degradable Polymer Wrapping and Efficient Removal Techniques

Semiconducting carbon nanotubes (s-CNTs) have emerged as a promising alternative to traditional silicon for ultrascaled field-effect transistors (FETs), owing to their exceptional properties. Aligned s-CNTs (A-CNTs) are particularly favored for practical applications due to their ability to provide higher driving current and lower contact resistance compared with individual s-CNTs or random networks. Achieving high-semiconducting-purity A-CNTs typically involves conjugated polymer wrapping for selective separation of s-CNTs, followed by self-assembly techniques. However, the presence of the polymer wrapper on A-CNTs can adversely impact electrical contact, gating efficiency, carrier transport, and device-to-device variations, necessitating its complete removal. While various methods have been explored for polymer removal, accurately characterizing the extent of removal remains a challenge. Traditional techniques such as absorption spectroscopy and X-ray photoelectron spectroscopy (XPS) may not accurately depict the remaining polymer content on A-CNTs due to their inherent detection limits. Consequently, the performance of FETs based on pure polymer-wrapper-free A-CNTs is unclear. In this study, we present an approach for preparing high-semiconducting-purity and polymer-wrapper-free A-CNTs using poly[(9,9-dioctylfluorenyl-2,7-dinitrilomethine)-(9,9-dioctylfluorenyl-2,7-dimethine)] (PFO-N-PFO), a degradable polymer, in conjunction with a modified dimension-limited self-alignment process (m-DLSA). Comprehensive transmission electron microscopy (TEM) characterizations, complemented by absorption and XPS characterizations, provide robust evidence of the successful near-complete removal of the polymer wrapper via a cleaning procedure involving acidic degradation, hot solvent rinsing, and vacuum annealing. Furthermore, top-gated FETs based on these high-semiconducting-purity and polymer-wrapper-free A-CNTs exhibit good performance metrics, including an on-current (Ion) of 2.2 mA/μm, peak transconductance (gm) of 1.1 mS/μm, low contact resistance (Rc) of 191 Ω·μm, and negligible hysteresis, representing a significant advancement in the CNT-based FET technology.

Recent Advances in Research from Nanoparticle to Nano-Assembly: A Review

The careful arrangement of nanomaterials (NMs) holds promise for revolutionizing various fields, from electronics and biosensing to medicine and optics. This review delves into the intricacies of nano-assembly (NA) techniques, focusing on oriented-assembly methodologies and stimuli-dependent approaches. The introduction provides a comprehensive overview of the significance and potential applications of NA, setting the stage for review. The oriented-assembly section elucidates methodologies for the precise alignment and organization of NMs, crucial for achieving desired functionalities. The subsequent section delves into stimuli-dependent techniques, categorizing them into chemical and physical stimuli-based approaches. Chemical stimuli-based self-assembly methods, including solvent, acid-base, biomolecule, metal ion, and gas-induced assembly, are discussed in detail by presenting examples. Additionally, physical stimuli such as light, magnetic fields, electric fields, and temperature are examined for their role in driving self-assembly processes. Looking ahead, the review outlines futuristic scopes and perspectives in NA, highlighting emerging trends and potential breakthroughs. Finally, concluding remarks summarize key findings and underscore the significance of NA in shaping future technologies. This comprehensive review serves as a valuable resource for researchers and practitioners, offering insights into the diverse methodologies and potential applications of NA in interdisciplinary research fields.

Simulation of Novel Nano Low-Dimensional FETs at the Scaling Limit

The scaling of bulk Si-based transistors has reached its limits, while novel architectures such as FinFETs and GAAFETs face challenges in sub-10 nm nodes due to complex fabrication processes and severe drain-induced barrier lowering (DIBL) effects. An effective strategy to avoid short-channel effects (SCEs) is the integration of low-dimensional materials into novel device architectures, leveraging the coupling between multiple gates to achieve efficient electrostatic control of the channel. We employed TCAD simulations to model multi-gate FETs based on various dimensional systems and comprehensively investigated electric fields, potentials, current densities, and electron densities within the devices. Through continuous parameter scaling and extracting the sub-threshold swing (SS) and DIBL from the electrical outputs, we offered optimal MoS2 layer numbers and single-walled carbon nanotube (SWCNT) diameters, as well as designed structures for multi-gate FETs based on monolayer MoS2, identifying dual-gate transistors as suitable for high-speed switching applications. Comparing the switching performance of two device types at the same node revealed CNT's advantages as a channel material in mitigating SCEs at sub-3 nm nodes. We validated the performance enhancement of 2D materials in the novel device architecture and reduced the complexity of the related experimental processes. Consequently, our research provides crucial insights for designing next-generation high-performance transistors based on low-dimensional materials at the scaling limit.

Nonideality in Arrayed Carbon Nanotube Field Effect Transistors Revealed by High-Resolution Transmission Electron Microscopy

High density and high semiconducting-purity single-walled carbon nanotube array (A-CNT) have recently been demonstrated as promising candidates for high-performance nanoelectronics. Knowledge of the structures and arrangement of CNTs within the arrays and their interfaces to neighboring CNTs, metal contacts, and dielectrics, as the key components of an A-CNT field effect transistor (FET), is essential for device mechanistic understanding and further optimization, particularly considering that the current technologies for the fabrication of A-CNT wafers are mainly laboratory-level solution-based processes. Here, we conduct a systematic investigation into the microstructures of A-CNT FETs mainly via cross-sectional high-resolution transmission electron microscopy and tentatively establish a framework consisting of up to 11 parameters which can be used for structure-side quality evaluation of the A-CNT FETs. The parameter ensemble includes the diameter, length (or terminal), and density distribution of CNTs, radial deformation of CNTs, array alignment defects, surface crystallography facets of contact metal, thickness distribution of high-k dielectrics (HfO2), and the contact ratios for the CNT-CNT, CNT-metal, CNT-dielectric, and CNT-substrate interfaces. Enriched array alignment defects, i.e., bundle, stacking, misorientation, and voids, are observed with a total ratio sometimes up to ∼90% in pristine A-CNTs and even up to ∼95% after the device fabrication process. Thus, they are suggested as the prevalent performance-limiting factors for A-CNT FETs. Complex interfacial structures are observed at the CNT-CNT, CNT-metal contact, and CNT-high-k dielectric interfaces, making the local environment and the property of each component CNT involved in an A-CNT FET distinct from others in terms of the diameters, radial deformation, and interactions with the local surroundings (mainly through van der Waals interactions). The present study suggests further improvements on the fabrication technology of A-CNT wafers and devices and mechanistic investigations into the impacts of complex array alignment defects and interface structures on the electrical performance of A-CNT FETs as well.

A disposable immunosensor array using cellulose paper assembled chemiresistive biosensor for simultaneous monitoring of mycotoxins AFB1 and FB1

Due to the common contamination of multiple mycotoxins in food, which results in stronger toxicity, it is particularly important to simultaneously test for various mycotoxins for the protection of human health. In this study, a disposable immunosensor array with low-cost was designed and fabricated using cellulose paper, polydimethylsiloxane (PDMS), and semiconducting single-walled carbon nanotubes (s-SWCNTs), which was modified with specific antibodies for mycotoxins AFB1 and FB1 detection. The strategy for fabricating the immunosensor array with two individual channels involved a two-step protocol starting with the form of two kinds of carbon films by depositing single-wall carbon nanotubes (SWCNTs) and s-SWCNTs on the cellulose paper as the conductive wire and sensing element, followed by the assembly of chemiresistive biosensor with SWCNTs strip as the wire and s-SWCNTs as the sensing element. After immobilizing AFB1-bovine serum albumin (AFB1-BSA) and FB1-bovine serum albumin (FB1-BSA) separately on the different sensing regions, the formation of mycotoxin-BSA-antibody immunocomplexes transfers to electrochemical signal, which would change with the different concentrations of free mycotoxins. Under optimal conditions, the immunosensor array achieved a limit of detection (LOD) of 0.46 pg/mL for AFB1 and 0.34 pg/mL for FB1 within a wide dynamic range from 1 pg/mL to 20 ng/mL. Furthermore, the AFB1 and FB1 spiked in the ground corn and wheat extracts were detected with satisfactory recoveries, demonstrating the excellent practicality of this established method for simultaneous detection of mycotoxins.

Universalized and robust length separation of carbon and boron nitride nanotubes with improved polymer depletion-based fractionation

Partitioning nanoparticles by shape and dimension is paramount for advancing nanomaterial standardization, fundamental colloidal investigations, and technologies such as biosensing and digital electronics. Length-separation methods for single-walled carbon nanotubes (SWCNTs) have historically incurred trade-offs in precision and mass throughput, and boron nitride nanotubes (BNNTs) are a rapidly emerging material analogue. We extend and detail a polymer precipitation-based method to fractionate populations of either nanotube type at significant mass scale for four distinct nanotube sources of increasing average diameter (0.7 nm to >2 nm). Such separations result in a supernant phase containing shorter nanotubes and a pellet phase containing the longer nanotubes, with the threshold length for depletion decreasing with increasing polymer concentration. Cross-comparison through analytical ultracentrifugation, spectroscopy, and microscopy versus applied polymer concentration show tailorable and precise length fractionation for 100 nm through >1 μm rod lengths, with fractionation also designable to remove non-nanotube impurities. The threshold length of depletion is further found to increase for decreasing nanotube diameter at fixed polymer concentration, a finding consistent with scaling attributable to nanotube radial excluded volume. The capabilities demonstrated herein promise to significantly advance nanotube implementation within the scientific community.

Floating Bimetallic Catalysts for Growing 30 cm-Long Carbon Nanotube Arrays with High Yields and Uniformity

Ultralong carbon nanotubes (CNTs) are considered as promising candidates for many cutting-edge applications. However, restricted by the extremely low yields of ultralong CNTs, their practical applications can hardly be realized. Therefore, new methodologies shall be developed to boost the growth efficiency of ultralong CNTs and alleviate their areal density decay at the macroscale level. Herein, a facile, universal, and controllable method for the in situ synthesis of floating bimetallic catalysts (FBCs) is proposed to grow ultralong CNT arrays with high yields and uniformity. Ferrocene and metal acetylacetonates serve as catalyst precursors, affording the successful synthesis of a series of FBCs with controllable compositions. Among these FBCs, the optimized FeCu catalyst increases the areal density of ultralong CNT arrays to a record-breaking value of ≈8100 CNTs mm-1 and exhibits a lifetime 3.40 times longer than that of Fe, thus achieving both high yields and uniformity. A 30-centimeters-long and high-density ultralong CNT array is also successfully grown with the assistance of FeCu catalysts. As evidenced by this kinetic model and molecular dynamics simulations, the introduction of Cu into Fe can simultaneously improve the catalyst fluidity and decrease carbon solubility, and an optimal catalytic performance will be achieved by balancing this tradeoff.

Removing Conjugated Polymers from Aligned Carbon Nanotube Arrays

Aligned carbon nanotube (A-CNT) with high semiconducting purity and high-density have been considered as one of the most promising active channels for field-effect transistors (FETs), but conjugated polymer dispersant residues on the surface of A-CNT have become the main obstacle for its further development in electronics applications. In this work, a series of removable conjugated polymers (CPs) are designed and synthesized to achieve favorable purification and alignment for CNT arrays with a high density of ≈360 CNTs/µm. Furthermore, a removal process of CPs on the CNT array film is developed. Raman spectra show that the CNTs in array film are almost not damaged after the removal process, and the G/D ratio is as high as 35. The field-effect transistors (FETs) are fabricated with a saturation current density up to 600 µA µm-1 and a current on-off ratio of ≈105, even with a relatively long channel length of ≈3 µm.

Inner Doping of Carbon Nanotubes with Perovskites for Ultralow Power Transistors

Semiconducting carbon nanotubes (CNTs) are considered as the most promising channel material to construct ultrascaled field-effect transistors, but the perfect sp2 C─C structure makes stable doping difficult, which limits the electrical designability of CNT devices. Here, an inner doping method is developed by filling CNTs with 1D halide perovskites to form a coaxial heterojunction, which enables a stable n-type field-effect transistor for constructing complementary metal-oxide-semiconductor electronics. Most importantly, a quasi-broken-gap (BG) heterojunction tunnel field-effect transistor (TFET) is first demonstrated based on an individual partial-filling CsPbBr3/CNT and exhibits a subthreshold swing of 35 mV dec-1 with a high on-state current of up to 4.9 µA per tube and an on/off current ratio of up to 105 at room temperature. The quasi-BG TFET based on the CsPbBr3/CNT coaxial heterojunction paves the way for constructing high-performance and ultralow power consumption integrated circuits.

Systematic Selection of High-Affinity ssDNA Sequences to Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) have gained significant interest for their potential in biomedicine and nanoelectronics. The functionalization of SWCNTs with single-stranded DNA (ssDNA) enables the precise control of SWCNT alignment and the development of optical and electronic biosensors. This study addresses the current gaps in the field by employing high-throughput systematic selection, enriching high-affinity ssDNA sequences from a vast random library. Specific base compositions and patterns are identified that govern the binding affinity between ssDNA and SWCNTs. Molecular dynamics simulations validate the stability of ssDNA conformations on SWCNTs and reveal the pivotal role of hydrogen bonds in this interaction. Additionally, it is demonstrated that machine learning could accurately distinguish high-affinity ssDNA sequences, providing an accessible model on a dedicated webpage (http://service.k-medai.com/ssdna4cnt). These findings open new avenues for high-affinity ssDNA-SWCNT constructs for stable and sensitive molecular detection across diverse scientific disciplines.

Wafer-Scale Fabrication of Wearable All-Carbon Nanotube Photodetector Arrays

With electronic devices evolving toward portable and high-performance wearables, the constraints of complex and wet processing technologies become apparent. This study presents a scalable photolithography/chemical-free method for crafting wearable all-carbon nanotube (CNT) photodetector device arrays. Laser-assisted patterning and dry deposition techniques directly assemble gas-phase CNTs into flexible devices without any lithography or lift-off processes. The resulting wafer-scale all-CNT photodetector arrays showcase excellent uniformity, wearability, environmental stability, and notable broadband photoresponse, boasting a high responsivity of 44 AW-1 and a simultaneous detectivity of 1.9 × 109 Jones. This research provides an efficient, versatile, and scalable strategy for manufacturing wearable all-CNT device arrays, allowing widespread adoption in wearable optoelectronics and multifunctional sensors.

Interface States in Gate Stack of Carbon Nanotube Array Transistors

A deep understanding of the interface states in metal-oxide-semiconductor (MOS) structures is the premise of improving the gate stack quality, which sets the foundation for building field-effect transistors (FETs) with high performance and high reliability. Although MOSFETs built on aligned semiconducting carbon nanotube (A-CNT) arrays have been considered ideal energy-efficient successors to commercial silicon (Si) transistors, research on the interface states of A-CNT MOS devices, let alone their optimization, is lacking. Here, we fabricate MOS capacitors based on an A-CNT array with a well-designed layout and accurately measure the capacitance-voltage and conductance-voltage (C-V and G-V) data. Then, the gate electrostatics and the physical origins of interface states are systematically analyzed and revealed. In particular, targeted improvement of gate dielectric growth in the A-CNT MOS device contributes to suppressing the interface state density (Dit) to 6.1 × 1011 cm-2 eV-1, which is a record for CNT- or low-dimensional semiconductors-based MOSFETs, boosting a record transconductance (gm) of 2.42 mS/μm and an on-off ratio of 105. Further decreasing Dit below 1 × 1011 cm-2 eV-1 is necessary for A-CNT MOSFETs to achieve the expected high energy efficiency.

Advancements and Challenges in the Integration of Indium Arsenide and Van der Waals Heterostructures

The strategic integration of low-dimensional InAs-based materials and emerging van der Waals systems is advancing in various scientific fields, including electronics, optics, and magnetics. With their unique properties, these InAs-based van der Waals materials and devices promise further miniaturization of semiconductor devices in line with Moore's Law. However, progress in this area lags behind other 2D materials like graphene and boron nitride. Challenges include synthesizing pure crystalline phase InAs nanostructures and single-atomic-layer 2D InAs films, both vital for advanced van der Waals heterostructures. Also, diverse surface state effects on InAs-based van der Waals devices complicate their performance evaluation. This review discusses the experimental advances in the van der Waals epitaxy of InAs-based materials and the working principles of InAs-based van der Waals devices. Theoretical achievements in understanding and guiding the design of InAs-based van der Waals systems are highlighted. Focusing on advancing novel selective area growth and remote epitaxy, exploring multi-functional applications, and incorporating deep learning into first-principles calculations are proposed. These initiatives aim to overcome existing bottlenecks and accelerate transformative advancements in integrating InAs and van der Waals heterostructures.

An enzymolysis-induced energy transfer co-assembled system for spontaneously recoverable supramolecular dynamic memory

The continuing growth of the digital world requires new ways of constructing memory devices to process and store dynamic data, because the current ones suffer from inefficiency, limited reads, and difficulty to manufacture. Here we propose a supramolecular dynamic memory (SDM) strategy based on an enzymolysis-induced energy transfer co-assembly derived from a naphthalene-based cationic monomer and organic dye sulforhodamine 101, enabling the construction of spontaneously recoverable dynamic memory devices. Benefitting from the large exciton migration rate (4.48 × 1015 L mol-1 s-1) between the monomer and sulforhodamine 101, the energy transfer process between the two is effectively achieved. Since alkaline phosphatase can selectively hydrolyze adenosine triphosphate, leading to the disruption of the co-assemblies, an enzyme-mediated time-dependent fluorochromic system is realized. On this basis, a SDM system featuring spontaneous recovery and enabling the memory of dynamic information in optical and electrical modes is successfully constructed. The current study represents a promising step in the nascent development of supramolecular materials for computational systems.

Semiconducting Carbon Nanotube Extraction Enabled by Alkylated Cellulose Wrapping

With the growing demand for postsilicon electronics, the purification of single-walled carbon nanotubes (SWCNTs) in terms of their chirality, which defines their atomic and electronic structure, is becoming increasingly important. Herein, we demonstrate the selective extraction of high-quality semiconducting SWCNTs using alkyl cellulose as a dispersant in organic solvents. We investigated the separation factors of dispersant structures, such as the degree of substitution (DS) and molecular weight, and clarified the appropriate dispersant structures, such as moderately substituted hexyl cellulose, for selective semiconducting SWCNT extraction. Due to the improved purity and quality of the semiconducting SWCNTs obtained by this method, their films exhibit excellent thermoelectric power factors, outperforming not only unsorted SWCNTs but also conducting polymer-sorted SWCNTs. This sorting technology paves the way for supplying high-quality semiconducting SWCNTs in a viable manner.

Establishing Ohmic Contact of a Radial Compressed CNT Bundle with High Work Function Metal

Establishing low-resistance ohmic contact is critical for developing electronic devices based on traditional silicon and new low-dimensional materials. Due to unprecedented electronic and mechanical properties, the one-dimensional carbon nanotubes (CNTs) have been used as source/drain, gate, or tunnel to fabricate transistors. However, the mechanism causing low-resistance ohmic contact is not clear yet. Here, the hybrid atomic force microscopy-scanning electron microscopy (AFM-SEM) instrument was developed to establish lower-resistance ohmic contact between a radial compressed deformed multiwalled CNT bundle and high work function metal (platinum and gold). The radial compression structure under strong van der Waals attraction was in situ characterized through the SEM image to obtain the diameter and width and through AFM to get height and to perform nanoindentation, indicating that Pt has the smaller radial compression deformation. Molecular dynamics simulations exhibit that compared to Pt, a wider ribbon-like graphene layer formed when the radial compressed CNTs contacted with Au. The bond forming and electron orbital overlapping between C atoms of deformed CNTs and the high work function metal atom is beneficial for good electrical contact.

Biomimetic wafer-scale alignment of tellurium nanowires for high-mobility flexible and stretchable electronics

Flexible and stretchable thin-film transistors (TFTs) are crucial in skin-like electronics for wearable and implantable applications. Such electronics are usually constrained in performance owing to a lack of high-mobility and stretchable semiconducting channels. Tellurium, a rising semiconductor with superior charge carrier mobilities, has been limited by its intrinsic brittleness and anisotropy. Here, we achieve highly oriented arrays of tellurium nanowires (TeNWs) on various substrates with wafer-scale scalability by a facile lock-and-shear strategy. Such an assembly approach mimics the alignment process of the trailing tentacles of a swimming jellyfish. We further apply these TeNW arrays in high-mobility TFTs and logic gates with improved flexibility and stretchability. More specifically, mobilities over 100 square centimeters per volt per second and on/off ratios of ~104 are achieved in TeNW-TFTs. The TeNW-TFTs on polyethylene terephthalate can sustain an omnidirectional bending strain of 1.3% for more than 1000 cycles. Furthermore, TeNW-TFTs on an elastomeric substrate can withstand a unidirectional strain of 40% with no performance degradation.

Aligned carbon nanotube-based electronics on glass wafer

Carbon nanotubes (CNTs), due to excellent electronic properties, are emerging as a promising semiconductor for diverse electronic applications with superiority over silicon. However, until now, the supposed superiority of CNTs by "head-to-head" comparison within a well-defined voltage range remains unrealized. Here, we report aligned CNT (ACNT)-based electronics on a glass wafer and successfully develop a 250-nm gate length ACNT-based field-effect transistor (FET) with an almost identical transfer curve to a "90-nm" node silicon device, indicating a three- to four-generation superiority. Moreover, a record gate delay of 9.86 ps is achieved by our ring oscillator, which exceeds silicon even at a lower supply voltage. Furthermore, the fabrication of basic logic gates indicates the potential for further digital integrated circuits. All of these results highlight ACNT-based FETs on the glass wafer as an effective solution/platform for further development of CNT-based electronics.

Assembly and Alignment of High Packing Density Carbon Nanotube Arrays Using Lithographically Defined Microscopic Water Features

High packing density aligned arrays of semiconducting carbon nanotubes (CNTs) are required for many electronics applications. Past work has shown that the accumulation of CNTs at a water-solvent interface can drive array self-assembly. Previously, the confining interface was a large-area, macroscopic feature. Here, we report on the CNT assembly on microscopic water features. Water microdroplets are formed on 10-100 μm wide hydrophilic stripes patterned on a substrate. Exposure to CNTs dispersed in solvent accumulates CNTs at the microdroplet-solvent interface, driving their alignment and deposition at the microdroplet-solvent-substrate contact line. Compared with macroscopic methods in which the contact line uncontrollably moves across the substrate as it is pulled out of the liquids, the hydrophilic patterns and microdroplets allow pinning of the contact line. As CNTs deposit, the contact line self-translates, allowing for dense CNT packing. We realize monolayer CNT arrays aligned within ±3.9° at density of 250 μm-1 and field effect transistors with a high current density of 1.9 mA μm-1 and transconductance of 1.2 mS μm-1 at -0.6 V drain bias and 60 nm channel length.

New structure transistors for advanced technology node CMOS ICs

Over recent decades, advancements in complementary metal-oxide-semiconductor integrated circuits (ICs) have mainly relied on structural innovations in transistors. From planar transistors to the fin field-effect transistor (FinFET) and gate-all-around FET (GAAFET), more gate electrodes have been added to three-dimensional (3D) channels with enhanced control and carrier conductance to provide higher electrostatic integrity and higher operating currents within the same device footprint. Beyond the 1-nm node, Moore's law scaling is no longer expected to be applicable to geometrical shrinkage. Vertical transistor stacking, e.g. in complementary FETs (CFET), 3D stack (3DS) FETs and vertical-channel transistors (VFET), for enhanced density and variable circuit or system design represents a revolutionary scaling approach for sustained IC development. Herein, innovative works on specific structures, key process breakthroughs, shrinking cell sizes and design methodologies for transistor structure research and development are reviewed. Perspectives on future innovations in advanced transistors with new channel materials and operating theories are also discussed.

Road map for, and technical challenges of, carbon-nanotube integrated circuit technology

A new targeted observational algorithm was developed to optimize prediction targets across various regions and variables. This approach was utilized to design an optimal ENSO monitoring array in the TPOS 2020 project.

Low-dimensional nanostructures for monolithic 3D-integrated flexible and stretchable electronics

Flexible/stretchable electronics, which are characterized by their ultrathin design, lightweight structure, and excellent mechanical robustness and conformability, have garnered significant attention due to their unprecedented potential in healthcare, advanced robotics, and human-machine interface technologies. An increasing number of low-dimensional nanostructures with exceptional mechanical, electronic, and/or optical properties are being developed for flexible/stretchable electronics to fulfill the functional and application requirements of information sensing, processing, and interactive loops. Compared to the traditional single-layer format, which has a restricted design space, a monolithic three-dimensional (M3D) integrated device architecture offers greater flexibility and stretchability for electronic devices, achieving a high-level of integration to accommodate the state-of-the-art design targets, such as skin-comfort, miniaturization, and multi-functionality. Low-dimensional nanostructures possess small size, unique characteristics, flexible/elastic adaptability, and effective vertical stacking capability, boosting the advancement of M3D-integrated flexible/stretchable systems. In this review, we provide a summary of the typical low-dimensional nanostructures found in semiconductor, interconnect, and substrate materials, and discuss the design rules of flexible/stretchable devices for intelligent sensing and data processing. Furthermore, artificial sensory systems in 3D integration have been reviewed, highlighting the advancements in flexible/stretchable electronics that are deployed with high-density, energy-efficiency, and multi-functionalities. Finally, we discuss the technical challenges and advanced methodologies involved in the design and optimization of low-dimensional nanostructures, to achieve monolithic 3D-integrated flexible/stretchable multi-sensory systems.

Polymer removal and dispersion exchange of (10,5) chiral carbon nanotubes with enhanced 1.5 μm photoluminescence

Singe-chirality single-walled carbon nanotubes (SWCNTs) produced by selective polymer extraction have been actively investigated for their semiconductor applications. However, to fulfil the needs of biocompatible applications, the organic solvents in polymer-sorted SWCNTs impose a limitation. In this study, we developed a novel strategy for organic-to-aqueous phase exchange, which involves thoroughly removing polymers from the sorted SWCNTs, followed by surfactant covering and redispersing of the cleaned SWCNTs in water. Importantly, the obtained aqueous system allows us to perform sp3 functionalization of the SWCNTs, leading to a strong photoluminescence emission at 1550 nm from the defect sites of (10,5) SWCNTs. These functionalized SWCNTs as infrared light emitters show considerable potential for bioimaging applications. This exchange-and-functionalization strategy opens the door for future biocompatible applications of polymer-sorted SWCNTs.

Interlayer Charge Transfer Induced Electrical Behavior Transition in 1D AgI@sSWCNT van der Waals Heterostructures

The emergence of one-dimensional van der Waals heterostructures (1D vdWHs) opens up potential fields with unique properties, but precise synthesis remains a challenge. The utilization of mixed conductive types of carbon nanotubes as templates has imposed restrictions on the investigation of the electrical behavior and interlayer interaction of 1D vdWHs. In this study, we efficiently encapsulated silver iodide in high-purity semiconducting single-walled carbon nanotubes (sSWCNTs), forming 1D AgI@sSWCNT vdWHs. We characterized the semiconductor-metal transition and increased the carrier concentration of individual AgI@sSWCNTs via sensitive dielectric force microscopy and confirmed the results through electrical device tests. The electrical behavior transition was attributed to an interlayer charge transfer, as demonstrated by Kelvin probe force microscopy. Furthermore, we showed that this method of synthesizing 1D heterostructures can be extended to other metal halides. This work opens the door for the further exploration of the electrical properties of 1D vdWHs.

High-Performance Carbon Nanotube Thin-Film Transistor Technology

Semiconducting single-walled carbon nanotubes (CNTs) have ideal electronic, chemical, and mechanical properties and are ideal channel materials for constructing transistors in the post-Moore era. Experiments have shown that CNT-based planar CMOS transistors can be scaled down to sub-10 nm technology nodes, demonstrating excellent performance far exceeding the silicon limit. At the same time, CNT electronic technology is essentially a thin-film transistor technology, which enables the construction of chips on such substrates as glass and polymers with an area of several meters, providing technical support for large-area and flexible electronic applications. In addition, since CNT electronics technology involves only low-temperature processes (less than 400 °C), the monolithic 3D integration of logic and memory devices can be realized which can greatly improve the comprehensive performance of the chip and lead to a thousand-fold performance increase for special data structures, especially in AI applications.

Direct Writing of Aligned Carbon Nanotubes across a Trench

Aligned and suspended carbon nanotubes can outperform randomly oriented networks in electronic biosensing and thin-film electronics. However, carbon nanotubes tend to bundle and form random networks. Here, we show that carbon nanotubes spontaneously align in an ammonium deoxycholate surfactant gel even under low shear forces, allowing direct writing and printing of nanotubes into electrically conducting wires and aligned thin layers across trenches. To demonstrate its application potential, we directly printed arrays of disposable electrical biosensors, which show femtomolar sensitivity in the detection of DNA and SARS-CoV-2 RNA.

Band-to-Band Tunneling Leakage Current Characterization and Projection in Carbon Nanotube Transistors

Carbon nanotube (CNT) transistors demonstrate high mobility but also experience off-state leakage due to the small effective mass and band gap. The lower limit of off-current (IMIN) was measured in electrostatically doped CNT metal-oxide-semiconductor field-effect transistors (MOSFETs) across a range of band gaps (0.37 to 1.19 eV), supply voltages (0.5 to 0.7 V), and extension doping levels (0.2 to 0.8 carriers/nm). A nonequilibrium Green's function (NEGF) model confirms the dependence of IMIN on CNT band gap, supply voltage, and extension doping level. A leakage current design space across CNT band gap, supply voltage, and extension doping is projected based on the validated NEGF model for long-channel CNT MOSFETs to identify the appropriate device design choices. The optimal extension doping and CNT band gap design choice for a target off-current density are identified by including on-current projection in the leakage current design space. An extension doping level >0.5 carrier/nm is required for optimized on-current.

High-Speed Modulation of Polarized Thermal Radiation from an On-Chip Aligned Carbon Nanotube Film

Spectroscopic analysis with polarized light has been widely used to investigate molecular structure and material behavior. A broadband polarized light source that can be switched on and off at a high speed is indispensable for reading faint signals, but such a source has not been developed. Here, using aligned carbon nanotube (CNT) films, we have developed broadband thermal emitters of polarized infrared radiation with switching speeds of ≲20 MHz. We found that the switching speed depends on whether the electrical current is parallel or perpendicular to the CNT alignment direction with a significantly higher speed achieved in the parallel case. Together with detailed theoretical simulations, our experimental results demonstrate that the contact thermal conductance to the substrate and the conductance to the electrodes are important factors that determine the switching speed. These emitters can lead to advanced spectroscopic analysis techniques with polarized radiation.

Mixed-Solvent Engineering as a Way around the Trade-Off between Yield and Purity of (7,3) Single-Walled Carbon Nanotubes Obtained Using Conjugated Polymer Extraction

The inability to purify nanomaterials such as single-walled carbon nanotubes (SWCNTs) to the desired extent hampers the progress in nanoscience. Various SWCNT types can be purified by extraction, but it is challenging to establish conditions giving rise to the isolation of high-purity fractions. The problem stems from the fact that common organic solvents or water cannot provide an optimal environment for purification. Consequently, one must often decide between the separation yield and purity of the product. This article reports how through the self-synthesis of poly(9,9-dioctylfluorene-alt-benzothiadiazole) with tailored characteristics, in-depth elucidation of the extraction process, and mixed-solvent engineering, a high-yield isolation of monochiral (7,3) SWCNTs is developed. The combination of toluene and tetralin affords a separation medium of unique properties, wherein both high yield and exceptional purity can be attained simultaneously. The reported results pave the way for further research on this rare chirality, which, as illustrated herein, is much more reactive than any of the previously separated SWCNTs.

Confinement-induced nonlocality and casimir force in transdimensional systems

We study within the framework of the Lifshitz theory the long-range Casimir force for in-plane isotropic and anisotropic free-standing transdimensional material slabs. In the former case, we show that the confinement-induced nonlocality not only weakens the attraction of ultrathin slabs but also changes the distance dependence of the material-dependent correction to the Casimir force to go as contrary to the ∼1/l dependence of that of the local Lifshitz force. In the latter case, we use closely packed array of parallel aligned single-wall carbon nanotubes in a dielectric layer of finite thickness to demonstrate strong orientational anisotropy and crossover behavior for the inter-slab attractive force in addition to its reduction with decreasing slab thickness. We give physical insight as to why such a pair of ultrathin slabs prefers to stick together in the perpendicularly oriented manner, rather than in the parallel relative orientation as one would customarily expect.

0D van der Waals interfacial ferroelectricity

The dimensional limit of ferroelectricity has been long explored. The critical contravention is that the downscaling of ferroelectricity leads to a loss of polarization. This work demonstrates a zero-dimensional ferroelectricity by the atomic sliding at the restrained van der Waals interface of crossed tungsten disufilde nanotubes. The developed zero-dimensional ferroelectric diode in this work presents not only non-volatile resistive memory, but also the programmable photovoltaic effect at the visible band. Benefiting from the intrinsic dimensional limitation, the zero-dimensional ferroelectric diode allows electrical operation at an ultra-low current. By breaking through the critical size of depolarization, this work demonstrates the ultimately downscaled interfacial ferroelectricity of zero-dimensional, and contributes to a branch of devices that integrates zero-dimensional ferroelectric memory, nano electro-mechanical system, and programmable photovoltaics in one.

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.

Quartz Nonadherent and Clean Exfoliation of the Heteroatom-Doped Bulk Carbon Nanotubes Array

Vertically aligned carbon nanotubes array offers unique properties for various applications. Detaching them from the growth substrate, while preserving their vertical structure, is essential. Quartz, a cost-effective alternative to silicon wafers and metal-based substrates, can serve as both a reaction chamber and a growth substrate. However, the strong adhesive interaction with the quartz substrate remains an obstacle for further applications. Herein, we presented a simple and well-controlled exfoliation strategy assisted by the introduction of heteroatoms at root ends of a carbon nanotubes array. This strategy forms lower surface polarity of the carbon fragment to significantly reduce adhesion to the quartz substrate, which contributes to the effortless exfoliation. Furthermore, this scalable approach enables potential mass production on recyclable quartz substrates, enhancing the cost-effectiveness and efficiency. This work can establish a solid foundation for cost-competitive carbon nanotube-based technologies, offering a promising avenue for their widespread applications.

Direct Application of Carbon Nanotubes (CNTs) Grown by Chemical Vapor Deposition (CVD) for Integrated Circuits (ICs) Interconnection: Challenges and Developments

With the continuous shrinkage of integrated circuit (IC) dimensions, traditional copper interconnect technology is gradually unable to meet the requirements for performance improvement. Carbon nanotubes have gained widespread attention and research as a potential alternative to copper, due to their excellent electrical and mechanical properties. Among various methods for producing carbon nanotubes, chemical vapor deposition (CVD) has the advantages of mild reaction conditions, low cost, and simple reaction operations, making it the most promising approach to achieve compatibility with integrated circuit manufacturing processes. Combined with through silicon via (TSV), direct application of CVD-grown carbon nanotubes in IC interconnects can be achieved. In this article, based on the above background, we focus on discussing some of the main challenges and developments in the application of CVD-grown carbon nanotubes in IC interconnects, including low-temperature CVD, metallicity enrichment, and contact resistance.

Parameters Affecting Interfacial Assembly and Alignment of Nanotubes

Tangential flow interfacial self-assembly (TaFISA) is a promising scalable technique enabling uniformly aligned carbon nanotubes for high-performance semiconductor electronics. In this process, flow is utilized to induce global alignment in two-dimensional nematic carbon nanotube assemblies trapped at a liquid/liquid interface, and these assemblies are subsequently deposited on target substrates. Here, we present an observational study of experimental parameters that affect the interfacial assembly and subsequent aligned nanotube deposition. We specifically study the water contact angle (WCA) of the substrate, nanotube ink composition, and water subphase and examine their effects on liquid crystal defects, overall and local alignment, and nanotube bunching or crowding. By varying the substrate chemical functionalization, we determine that highly aligned, densely packed, individualized nanotubes deposit only at relatively small WCA between 35 and 65°. At WCA (< 10°), high nanotube bunching or crowding occurs, and the film is nonuniform, while aligned deposition ceases to occur at higher WCA (>65°). We find that the best alignment, with minimal liquid crystal defects, occurs when the polymer-wrapped nanotubes are dispersed in chloroform at a low (0.6:1) wrapper polymer to nanotube ratio. We also demonstrate that modifying the water subphase through the addition of glycerol not only improves overall alignment and reduces liquid crystal defects but also increases local nanotube bunching. These observations provide important guidance for the implementation of TaFISA and its use toward creating technologies based on aligned semiconducting carbon nanotubes.

Biotemplated precise assembly approach toward ultra-scaled high-performance electronics

Structural DNA nanotechnology can be programmed into complex designer structures with molecular precision for directing a wide range of inorganic and biological materials. However, the use of DNA-templated approaches for the fabrication and performance requirements of ultra-scaled semiconductor electronics is limited by its assembly disorder and destructive interface composition. In this protocol, using carbon nanotubes (CNTs) as model semiconductors, we provide a stepwise process to build ultra-scaled, high-performance field-effect transistors (FETs) from micron-scale three-dimensional DNA templates. We apply the approach to assemble CNT arrays with uniform pitches scaled between 24.1 and 10.4 nm with yields of more than 95%, which exceeds the resolution limits of conventional lithography. To achieve highly clean CNT interfaces, we detail a rinsing-after-fixing step to remove residual DNA template and salt contaminations present around the contact and the channel regions, without modifying the alignment of the CNT arrays. The DNA-templated CNT FETs display both high on-state current (4-15 μA per CNT) and small subthreshold swing (60-100 mV per decade), which are superior to previous examples of biotemplated electronics and match the performance metrics of high-performance, silicon-based electronics. The scalable assembly of defect-free three-dimensional DNA templates requires 1 week and the CNT arrays can be synthesized within half a day. The interface engineering requires 1-2 d, while the fabrication of high-performance FET and logic gate circuits requires 2-4 d. The structural and performance characterizations of molecular-precise DNA self-assembly and high-performance electronics requires 1-2 d. The protocol is suited for users with expertise in DNA nanotechnology and semiconductor electronics.

The future transistors

The metal-oxide-semiconductor field-effect transistor (MOSFET), a core element of complementary metal-oxide-semiconductor (CMOS) technology, represents one of the most momentous inventions since the industrial revolution. Driven by the requirements for higher speed, energy efficiency and integration density of integrated-circuit products, in the past six decades the physical gate length of MOSFETs has been scaled to sub-20 nanometres. However, the downscaling of transistors while keeping the power consumption low is increasingly challenging, even for the state-of-the-art fin field-effect transistors. Here we present a comprehensive assessment of the existing and future CMOS technologies, and discuss the challenges and opportunities for the design of FETs with sub-10-nanometre gate length based on a hierarchical framework established for FET scaling. We focus our evaluation on identifying the most promising sub-10-nanometre-gate-length MOSFETs based on the knowledge derived from previous scaling efforts, as well as the research efforts needed to make the transistors relevant to future logic integrated-circuit products. We also detail our vision of beyond-MOSFET future transistors and potential innovation opportunities. We anticipate that innovations in transistor technologies will continue to have a central role in driving future materials, device physics and topology, heterogeneous vertical and lateral integration, and computing technologies.

High-Speed Carbon Nanotube Photodetectors for 2 μm Communications

In the era of big data, the growing demand for data transmission capacity requires the communication band to expand from the traditional optical communication windows (∼1.3-1.6 μm) to the 2 μm band (1.8-2.1 μm). However, the largest bandwidth (∼30 GHz) of the current high-speed photodetectors for the 2 μm window is considerably less than the developed 1.55 μm band photodetectors based on III-V materials or germanium (>100 GHz). Here, we demonstrate a high-performance carbon nanotube (CNT) photodetector that can operate in both the 2 and 1.55 μm wavelength bands based on high-density CNT arrays on a quartz substrate. The CNT photodetector exhibits a high responsivity of 0.62 A/W and a large 3 dB bandwidth of 40 GHz (setup-limited) at 2 μm. The bandwidth is larger than that of existing photodetectors working in this wavelength range. Moreover, the CNT photodetector operating at 1.55 μm exhibits a setup-limited 3 dB bandwidth over 67 GHz at zero bias. Our work indicates that CNT photodetectors with high performance and low cost have great potential for future high-speed optical communication at both the 2 and 1.55 μm bands.

Aligned Carbon Nanotubes-Based Radiofrequency Transistors for Amplitude Amplification and Frequency Conversion at Millimeter Wave Band

Aligned carbon nanotubes (ACNTs) have been considered as a promising candidate semiconductor with great potential in radiofrequency (RF) electronics due to their high carrier mobility/saturation velocity and small intrinsic capacitance. However, almost all of previously reported works focused on only the cutoff frequency, which is far from enough for practical RF application. In this work, given the speed advantage of ACNTs, we further explore amplitude amplification and frequency conversion capability of ACNTs based RF devices simultaneously, which are two basic functions in RF electronics. Considering there is no de-embedding process for amplification/conversion and reduction power loss, multifinger configuration RF transistors (still having current density around 1 mA/μm) were fabricated with cutoff frequency and maximum oscillation frequency exceeding 150 and 130 GHz, respectively. Based on dedicated ACNTs based RF FETs, we demonstrate almost 7 dB power gain (S₂₁) with over 40 GHz 3-dB bandwidth for amplification and from -12.7 to -17 dB of conversion gain with over 25 dBm IIP3 (input third-order intercept point) of linearity for conversion simultaneously operating at 30 GHz in millimeter wave (mmWave) band both without any tuning instruments and matching technology assistance. The performance achieved here is the best among all the nanomaterials at the mmWave band.