Unzipping Carbon Nanotubes to Sub-5-nm Graphene Nanoribbons on Cu(111) by Surface Catalysis

Graphene nanoribbons (GNRs) are promising in nanoelectronics for their quasi-1D structures with tunable bandgaps. The methods for controllable fabrication of high-quality GNRs are still limited. Here a way to generate sub-5-nm GNRs by annealing single-walled carbon nanotubes (SWCNTs) on Cu(111) is demonstrated. The structural evolution process is characterized by low-temperature scanning tunneling microscopy. Substrate-dependent measurements on Au(111) and Ru(0001) reveal that the intermediate strong SWCNT-surface interaction plays a pivotal role in the formation of GNRs.

Wafer-Scale Carbon Nanotubes Diodes Based on Dielectric-Induced Electrostatic Doping

Diodes based on p-n junctions are fundamental building blocks for numerous circuits, including rectifiers, photovoltaic cells, light-emitting diodes (LEDs), and photodetectors. However, conventional doping techniques to form p- or n-type semiconductors introduce impurities that lead to Coulomb scattering. When it comes to low-dimensional materials, controllable and stable doping is challenging due to the feature of atomic thickness. Here, by selectively depositing dielectric layers of Y2O3 and AlN, direct formation of wafer-scale carbon-nanotube (CNT) diodes are demonstrated with high yield and spatial controllability. It is found that the oxygen interstitials in Y2O3, and the oxygen vacancy together with Al-Al bond in AlN/Y2O3 electrostatically modulate the intrinsic CNTs channel, which leads to p- and n-type conductance, respectively. These CNTs diodes exhibit a high rectification ratio (>104) and gate-tunable rectification behavior. Based on these results, we demonstrate the applicability of the diodes in electrostatic discharge (ESD) protection and photodetection.

Improving Carbon Nanotube-Based Radiofrequency Field-Effect Transistors by the Device Architecture and Doping Process

The semiconducting carbon nanotube (CNT) has been considered a promising candidate for future radiofrequency (RF) electronics due to its excellent electrical properties of high mobility and small capacitance. After decades of development, great progress has been achieved on CNT-based RF field-effect transistors (FETs). However, almost all elevations are owing to advancement of the CNT materials and fabrication process, while the study of device architecture is seldom considered and reported. In this work, we innovatively combined device architecture and related doping processes to further optimize CNT-based RF FETs by guiding process or materials with collaborative optimization for the first time and explore their effect on device performance carefully and statistically. Based on more mature random-oriented CNT materials, we fabricated CNT-based RF FETs having three different gate positions of device architecture variation accompanied by suitable doping schemes. The optimized FETs obtained 2-3 times of current density (transconductance) and 1.3 times the cutoff frequency and maximum oscillation frequency compared with unoptimized devices at the same channel length. After transistor-level verification of effect, we further built a CNT RF amplifier and demonstrated almost 10 dB of transducer gain improvement operating at 8 GHz for X-band application. The achieved results from this work would help further improve CNT RF performance beyond the materials and process point of view.

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.

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.

Amplification-Free Detection of SARS-CoV-2 Down to Single Virus Level by Portable Carbon Nanotube Biosensors

The rapid and sensitive detection of trace-level viruses in a simple and reliable way is of great importance for epidemic prevention and control. Here, a multi-functionalized floating gate carbon nanotube field effect transistor (FG-CNT FET) based biosensor is reported for the single virus level detection of SARS-CoV-2 virus antigen and RNA rapidly with a portable sensing platform. The aptamers functionalized sensors can detect SARS-CoV-2 antigens from unprocessed nasopharyngeal swab samples within 1 min. Meanwhile, enhanced by a multi-probe strategy, the FG-CNT FET-based biosensor can detect the long chain RNA directly without amplification down to single virus level within 1 min. The device, constructed with packaged sensor chips and a portable sensing terminal, can distinguish 10 COVID-19 patients from 10 healthy individuals in clinical tests both by the RNAs and antigens by a combination detection strategy with an combined overall percent agreement (OPA) close to 100%. The results provide a general and simple method to enhance the sensitivity of FET-based biochemical sensors for the detection of nucleic acid molecules and demonstrate that the CNT FG FET biosensor is a versatile and reliable integrated platform for ultrasensitive multibiomarker detection without amplification and has great potential for point-of-care (POC) clinical tests.

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.

Silicon Waveguide-Integrated Carbon Nanotube Photodetector with Low Dark Current and 48 GHz Bandwidth

Low-dimensional materials with excellent optoelectronic properties and complementary metal-oxide-semiconductor (CMOS) process compatibility have the potential to construct high-performance photodetectors used in a cost-efficient monolithic or hybrid integrated optical communication system. Carbon nanotubes (CNTs) have attracted a lot of attention due to special geometric structure and broad band response, high optical absorption coefficient, ps-level intrinsic light response, high carrier mobility and wafer-scaled production process. Here, we demonstrated a high-performance waveguide-integrated CNT photodetector with asymmetric palladium (Pd) and hafnium (Hf) contact electrodes. The ideal photodetector structure was realized via comparing with simulation and experimental results, where the optimized device achieved a high 3 dB bandwidth ∼48 GHz at 0 V, as well as a responsivity ∼73.62 mA/W and dark current ∼0.157 μA at -2 V bias voltage. This waveguide-integrated CNT photodetector with low dark current and high bandwidth is helpful for next-generation optical communication and high-speed optical interconnects.

An Ultrathin Flexible Programmable Spin Logic Device Based on Spin-Orbit Torque

Flexible electronic devices have shown increasingly promising value facilitating our daily lives. However, flexible spintronic devices remain in their infancy. Here, this research demonstrates a type of nonvolatile, low power dissipation, and programmable flexible spin logic device, which is based on the spin-orbit torque in polyimide (PI)/Ta/Pt/Co/Pt heterostructures fabricated via capillary-assisted electrochemical delamination. The magnetization switching ratio is shown to be about 50% for the flexible device and does not change after 100 cycles of bending, indicating the device has stable performance. By designing the path of pulse current, five Boolean logic gates AND, NAND, NOT, NOR, and OR can be realized in an integrated two-element device. Moreover, such peeling-off devices can be successfully transferred to almost any substrate, such as paper and human skin, and maintain high performance. The flexible PI/Ta/Pt/Co/Pt spin logic device serves as logic-in-memory architecture and can be used in wearable electronics.

Ballistic two-dimensional InSe transistors

The International Roadmap for Devices and Systems (IRDS) forecasts that, for silicon-based metal-oxide-semiconductor (MOS) field-effect transistors (FETs), the scaling of the gate length will stop at 12 nm and the ultimate supply voltage will not decrease to less than 0.6 V (ref. 1). This defines the final integration density and power consumption at the end of the scaling process for silicon-based chips. In recent years, two-dimensional (2D) layered semiconductors with atom-scale thicknesses have been explored as potential channel materials to support further miniaturization and integrated electronics. However, so far, no 2D semiconductor-based FETs have exhibited performances that can surpass state-of-the-art silicon FETs. Here we report a FET with 2D indium selenide (InSe) with high thermal velocity as channel material that operates at 0.5 V and achieves record high transconductance of 6 mS μm-1 and a room-temperature ballistic ratio in the saturation region of 83%, surpassing those of any reported silicon FETs. An yttrium-doping-induced phase-transition method is developed for making ohmic contacts with InSe and the InSe FET is scaled down to 10 nm in channel length. Our InSe FETs can effectively suppress short-channel effects with a low subthreshold swing (SS) of 75 mV per decade and drain-induced barrier lowering (DIBL) of 22 mV V-1. Furthermore, low contact resistance of 62 Ω μm is reliably extracted in 10-nm ballistic InSe FETs, leading to a smaller intrinsic delay and much lower energy-delay product (EDP) than the predicted silicon limit.

Improving the Performance of Aligned Carbon Nanotube-Based Transistors by Refreshing the Substrate Surface

An aligned semiconducting carbon nanotube (A-CNT) array has been considered an excellent channel material to construct high-performance field-effect transistors (FETs) and integrated circuits (ICs). The purification and assembly processes to prepare a semiconducting A-CNT array require conjugated polymers, introducing stubborn residual polymers and stress at the interface between A-CNTs and substrate, which inevitably affects the fabrication and performance of the FETs. In this work, we develop a process to refresh the Si/SiO₂ substrate surface underneath the A-CNT film by wet etching to clean the residual polymers and release the stress. Top-gated A-CNT FETs fabricated with this process show significant performance improvement especially in terms of saturation on-current, peak transconductance, hysteresis, and subthreshold swing. These improvements are attributed to the increase in carrier mobility from 1025 to 1374 cm²/Vs by 34% after the substrate surface refreshing process. Representative 200 nm gate-length A-CNT FETs exhibit an on-current of 1.42 mA/μm and a peak transconductance of 1.06 mS/μm at a drain-to-source bias of 1 V, subthreshold swing (SS) of 105 mV/dec, and negligible hysteresis and drain-induced barrier lowering (DIBL) of 5 mV/V.

Ultra-Strong Comprehensive Radiation Effect Tolerance in Carbon Nanotube Electronics

Carbon nanotube (CNT) field-effect transistors (FETs) have been considered ideal building blocks for radiation-hard integrated circuits (ICs), the demand for which is exponentially growing, especially in outer space exploration and the nuclear industry. Many studies on the radiation tolerance of CNT-based electronics have focused on the total ionizing dose (TID) effect, while few works have considered the single event effects (SEEs) and displacement damage (DD) effect, which are more difficult to measure but may be more important in practical applications. Measurements of the SEEs and DD effect of CNT FETs and ICs are first executed and then presented a comprehensive radiation effect analysis of CNT electronics. The CNT ICs without special irradiation reinforcement technology exhibit a comprehensive radiation tolerance, including a 1 × 10⁴ MeVcm² mg^-1 level of the laser-equivalent threshold linear energy transfer (LET) for SEEs, 2.8 × 10¹³ MeV g^-1 for DD and 2 Mrad (Si) for TID, which are at least four times higher than those in conventional radiation-hardened ICs. The ultrahigh intrinsic comprehensive radiation tolerance will promote the applications of CNT ICs in high-energy solar and cosmic radiation environments.

Complementary Transistors Based on Aligned Semiconducting Carbon Nanotube Arrays

High-density semiconducting aligned carbon nanotube (A-CNT) arrays have been demonstrated with wafer-scale preparation of materials and have shown high performance in P-type field-effect transistors (FETs) and great potential for applications in future digital integrated circuits (ICs). However, high-performance N-type FETs (N-FETs) have not yet been implemented with A-CNTs, making development of complementary metal-oxide-semiconductor (CMOS) technology, a necessary component for modern digital ICs, impossible. In this work, we reveal the mechanism hindering the realization of A-CNT N-FETs contacted by low-work-function metals and develop corresponding solutions to promote the performance of N-FETs to that of P-type FETs (P-FETs). The fabricated scandium (Sc)-contacted A-CNT N-FET with a 100 nm gate length exhibits an on-state current (I_on) of 800 μA/μm and a peak transconductance (g_m) of 250 μS/μm, representing the highest performance of CNT-based N-FETs to date. Moreover, CMOS technology has been developed to realize N- and P-FETs with symmetric high performance based on A-CNTs. The fabricated A-CNT CMOS FETs show electron and hole mobilities of 325 and 241 cm² V^-1 s^-1, respectively, which are slightly higher than the corresponding values of Si CMOS transistors. Our scalable fabrication of A-CNT CMOS FETs with comparable electronic performance to Si CMOS will promote the application of CNT-based electronics in digital ICs.

An epidermal electronic system for physiological information acquisition, processing, and storage with an integrated flash memory array

Epidermal electronic systems that simultaneously provide physiological information acquisition, processing, and storage are in high demand for health care/clinical applications. However, these system-level demonstrations using flexible devices are still challenging because of obstacles in device performance, functional module construction, or integration scale. Here, on the basis of carbon nanotubes, we present an epidermal system that incorporates flexible sensors, sensor interface circuits, and an integrated flash memory array to collect physiological information from the human body surface; amplify weak biosignals by high-performance differential amplifiers (voltage gain of 27 decibels, common-mode rejection ratio of >43 decibels, and gain bandwidth product of >22 kilohertz); and store the processed information in the memory array with performance on par with industrial standards (retention time of 10⁸ seconds, program/erase voltages of ±2 volts, and endurance of 10⁶ cycles). The results shed light on the great application potential of epidermal electronic systems in personalized diagnostic and physiological monitoring.

Light-Controlled Reconfigurable Optical Synapse Based on Carbon Nanotubes/2D Perovskite Heterostructure for Image Recognition

Two-dimensional (2D) halide perovskite material is characterized by a mixed conducting behavior that possesses both electronic and ionic conductivity. The study on the influence of the light on ion migration in the 2D perovskite is helpful to improve the performance of perovskite-based optoelectronic devices. Here, we constructed an exfoliated 2D perovskite/carbon nanotubes (CNTs) heterostructure optical synapse, in which CNTs can be used as nanoprobes to qualitatively observe the ion aggregation or dissipation process in 2D perovskite, and found that light significantly changes the memory curve of the reconfigurable optical synapses. Through the molecular dynamic simulation, the dynamic process of ion migration in the heterostructure was simulated and the electrostatic interaction effect of nonequilibrium charge distribution of CNTs on iodide ion was demonstrated. Finally, an effective light-controlled process was realized through the synapses, which in situ regulated the performance of the weight-value discretized BP (WD-BP) neural network. This work lays a foundation for the future development of intelligent nano-optoelectronic devices.

Analyzing Gamma-Ray Irradiation Effects on Carbon Nanotube Top-Gated Field-Effect Transistors

Carbon nanotube (CNT) field-effect transistors (FETs) and integrated circuits (ICs) have been predicted and demonstrated to be some of the most promising candidates for radiation-hardened electronics. The studies mainly focused on the radiation response of the whole transistors, and experiments or analyses to reveal the detailed radiation responses of different components of the FET were absent. Here, we use a controllable experimental method to decouple the total ionizing dose (TID) radiation effects on different individual components of top-gate CNT FETs, including the CNT channel, gate dielectric, and substrate. The substrate is found to be more vulnerable to radiation damage than the gate dielectric and CNT film in FETs. Furthermore, the CNT film not only acts as a radiation-hardened semiconducting channel but also protects the channel/substrate interface by partially shielding the substrate from radiation damage. On the basis of the experimental data, a model is built to predict the irradiation resistance limit of CNT top-gated FETs, which can withstand at least 155 kGy irradiation.

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 (f_max), 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 f_max 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.

Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a diameter of around 1.0-1.5 nm, which present bandgaps comparable to silicon, are highly desired for electronic applications. Therefore, the preparation of s-SWCNTs of such diameters has been attracting great attention. The inner surface of SWCNTs has a suitable curvature and large contacting area, which is attractive in host-guest chemistry triggered by electron transfer. Here we reported a strategy of host-guest molecular interaction between SWCNTs and inner clusters with designed size, thus selectively separating s-SWCNTs of expected diameters. When polyoxometalate clusters of ∼1 nm in size were filled in the inner cavities of SWCNTs, s-SWCNTs with diameters concentrated at ∼1.3-1.4 nm were selectively extracted with the purity of ∼98% by a commercially available polyfluorene derivative. The field-effect transistors built from the sorted s-SWCNTs showed a typical behavior of semiconductors. The sorting mechanisms associated with size-dependent electron transfer from nanotubes to inner polyoxometalate were revealed by the spectroscopic and in situ electron microscopic evidence as well as the theoretical calculation. The polyoxometalates with designable size and redox property enable the flexible regulation of interaction between the nanotubes and the clusters, thus tuning the diameter of sorted s-SWCNTs. The present sorting strategy is simple and should be generally feasible in other SWCNT sorting techniques, bringing both great easiness in dispersant design and improved selectivity.

Ultrasensitive Magnetic Sensors Enabled by Heterogeneous Integration of Graphene Hall Elements and Silicon Processing Circuits

Graphene Hall elements (GHEs) have been demonstrated to be promising magnetic field sensors with excellent sensitivity, linearity, temperature stability, and compatibility with complementary-metal-oxide-semiconductor (CMOS)-integrated circuits (ICs). However, the demonstrated GHEs have still not exhibited a comprehensive advantage in performance over commercial integrated Hall sensors which were implemented in integrated Hall element and CMOS processing ICs. In this work, we develop a technology for the three-dimensional (3D) heterogeneous integration of silicon-based CMOS ICs and GHEs, and the fabricated magnetic field sensors outperform commercial high-end integrated Hall sensors. Specifically, the integrated Hall sensors are implemented in a stacked integration on Si based on a chopper programmable-gain amplifier (CPGA), a chopper-stabilized second-order sigma-delta modulator (CSDM), and graphene-based Hall elements on monochips. GHEs with high sensitivity (up to 1000 A/VT) are fabricated with a compatible process on a smoothened silicon nitride passivation layer of silicon-based CMOS ICs, and the two device layers are connected by an interlayer. The heterogeneous integrated Hall ICs exhibit current and voltage magnetic sensitivities up to 64 000 A/VT and 6.12 V/VT, respectively, which are much higher than those in all other reported nanomaterial-based Hall sensors and even in high-end commercial Hall ICs. Furthermore, the 3D heterogeneous integration technology used here can be extended as a universal technology for integrating nanomaterial-based sensors and Si CMOS ICs.

Strengthened Complementary Metal-Oxide-Semiconductor Logic for Small-Band-Gap Semiconductor-Based High-Performance and Low-Power Application

Silicon-based complementary metal-oxide-semiconductor (CMOS) has been the mainstream logic style for modern digital integrated circuits (ICs) for decades but will meet its performance limits soon. Extensive investigations have thus been carried out using other semiconductors, especially those with extremely high carrier mobility. However, these materials usually have small or even zero band gap, which leads inevitably to large leakage current or voltage loss in ICs based on these semiconductors. In this work, we propose and demonstrate a strengthened CMOS (SCMOS) logic style using modified field-effect transistors (FETs) to solve this problem, that is, to achieve high performance, utilizing the high carrier mobility in these materials, and to reduce the current leakage resulting from their small band gap. Conventional CMOS FETs are modified to have an asymmetric structure where an additional assistant gate is introduced near the drain to further lower the potential barrier in on-state and to increase the barrier in off-state. SCMOS ICs are constructed using these modified asymmetric CMOS FETs, which demonstrate perfect rail-to-rail output with negligible voltage loss and 3 orders of magnitude suppression of the static power consumption and an operating speed similar to or even higher than that of CMOS ICs. Here, SCMOS is demonstrated using carbon nanotubes, but, in principle, this logic style can be used in ICs based on any small-band-gap semiconductors to provide simultaneously high performance and low power consumption.

Wafer-Scale Uniform Carbon Nanotube Transistors for Ultrasensitive and Label-Free Detection of Disease Biomarkers

Carbon nanotube (CNT) field-effect transistor (FET)-based biosensors have shown great potential for ultrasensitive biomarker detection, but challenges remain, which include unsatisfactory sensitivity, difficulty in stable functionalization, incompatibility with scalable fabrication, and nonuniform performance. Here, we describe ultrasensitive, label-free, and stable FET biosensors built on polymer-sorted high-purity semiconducting CNT films with wafer-scale fabrication and high uniformity. With a floating gate (FG) structure using an ultrathin Y₂O₃ high-κ dielectric layer, the CNT FET biosensors show amplified response and improved sensitivity compared with those sensors without Y₂O₃, which is attributed to the chemical gate-coupling effect dominating the sensor response. The CNT FG-FETs are modified to selectively detect specific disease biomarkers, namely, DNA sequences and microvesicles, with theoretical record detection limits as low as 60 aM and 6 particles/mL, respectively. Furthermore, the biosensors exhibit highly uniform performance over the 4 in. wafer as well as superior bias stress stability. The FG CNT FET biosensors could be extended as a universal biosensor platform for the ultrasensitive detection of multiple biological molecules and applied in highly integrated and multiplexed all CNT-FET-based sensor architectures.

Silicon-Waveguide-Integrated Carbon Nanotube Optoelectronic System on a Single Chip

Monolithic optoelectronic integration based on a single material is a major pursuit in the fields of nanophotonics and nanoelectronics in order to meet the requirements of future fiber-optic telecommunication systems and on-chip optical interconnection systems. However, the incompatibility between silicon-based electronics and germanium or compound semiconductor-based photonics makes it very challenging to realize optoelectronic integration based on a single material. Here, the integration between silicon waveguides and a carbon nanotube (CNT) optoelectronic system is demonstrated. Waveguide-integrated photodetectors based on the CNT exhibit 12.5 mA/W photoresponsivity at 1530 nm, which presents an improvement of 97.6 times enhanced absorption efficiency compared to that without the waveguide. Multiplied output signals of cascading photodetectors are used to control the output of CNT-based logic gates, thereby demonstrating that the CNT-based optoelectronic integration system is compatible with silicon photonics. Our work indicates that carbon nanotubes have the potential for future integration between nanophotonics and nanoelectronics on a single chip.

Light-Enhanced Ion Migration in Two-Dimensional Perovskite Single Crystals Revealed in Carbon Nanotubes/Two-Dimensional Perovskite Heterostructure and Its Photomemory Application

Two-dimensional (2D) hybrid perovskite sandwiched between two long-chain organic layers is an emerging class of low-cost semiconductor materials with unique optical properties and improved moisture stability. Unlike conventional semiconductors, ion migration in perovskite is a unique phenomenon possibly responsible for long carrier lifetime, current-voltage hysteresis, and low-frequency giant dielectric response. While there are many studies of ion migration in bulk hybrid perovskite, not much is known for its 2D counterparts, especially for ion migration induced by light excitation. Here, we construct an exfoliated 2D perovskite/carbon nanotube (CNT) heterostructure field effect transistor (FET), not only to demonstrate its potential in photomemory applications, but also to study the light induced ion migration mechanisms. We show that the FET I-V characteristic curve can be regulated by light and shows two opposite trends under different CNT oxygen doping conditions. Our temperature-dependent study indicates that the change in the I-V curve is probably caused by ion redistribution in the 2D hybrid perovskite. The first principle calculation shows the reduction of the migration barrier of I vacancy under light excitation. The device simulation shows that the increase of 2D hybrid perovskite dielectric constant (enabled by the increased ion migration) can change the I-V curve in the trends observed experimentally. Finally, the so synthesized FET shows the multilevel photomemory function. Our work shows that not only we could understand the unique ion migration behavior in 2D hybrid perovskite, it might also be used for many future memory function related applications not realizable in traditional semiconductors.

Carbon Nanotube Film-Based Radio Frequency Transistors with Maximum Oscillation Frequency above 100 GHz

Carbon nanotubes (CNTs) have been considered a preferred channel material for constructing high-performance radio frequency (RF) transistors with outstanding current gain cutoff frequency (f_T) and power gain cutoff frequency (f_max) but the highest reported f_max is only 70 GHz. Here, we explore how good RF transistors based on solution-derived randomly oriented semiconducting CNT films, which are the most mature CNT materials for scalable fabrication of transistors and integrated circuits, can be achieved. Owing to the significantly reduced number of CNT/CNT junctions obtained by scaling the channel length down to below 100 nm, we realized RF field-effect transistors (FETs) with maximum transconductance G_m up to 0.38 mS/μm, which is the record among CNT-based RF FETs. After de-embedding the pad-induced capacitances and resistances, the CNT FETs with different gate lengths (L_g) exhibit f_T as high as 103 GHz (intrinsically 281 GHz) or f_max up to 107 GHz (intrinsically 190 GHz), which are the records among CNT-based RF FETs. In particular, the CNT FETs with an L_g of 50 nm present pad de-embedding f_T of 86 GHz and f_max of 85 GHz, and represent the best CNT RF transistor in terms of comprehensive performance to date. To demonstrate the actual high-speed and scalable fabrication of our CNT RF FETs, we fabricated CNT FET-based five-stage ring oscillators with oscillation frequencies above 5 GHz.

Tunable, Ultrasensitive, and Flexible Pressure Sensors Based on Wrinkled Microstructures for Electronic Skins

Flexible pressure sensors play an important role in electronic skins (E-Skins), which mimic the mechanical forces sensing properties of human skin. A rational design for a pressure sensor with adjustable characteristics is in high demand for different application scenarios. Here, we present tunable, ultrasensitive, and flexible pressure sensors based on compressible wrinkled microstructures. Modifying the morphology of polydimethylsiloxane (PDMS) microstructure enables the device to obtain different sensitivities and pressure ranges for different requirements. Furthermore, by intentionally introducing hollow structures in the PDMS wrinkles, our pressure sensor exhibits an ultrahigh sensitivity of 14.268 kPa^-1. The elastic microstructure-based capacitive sensor also possesses a very low detectable pressure limit (1.5 Pa), a fast response time (<50 ms), a wide pressure range, and excellent cycling stability. Implementing respiratory monitoring and vocalization recognition is realized by attaching the flexible pressure sensor onto the chest and throat, respectively, showing its great application potential for disease diagnosis, monitoring, and other advanced clinical/biological wearable technologies.

Improving the Performance and Uniformity of Carbon-Nanotube-Network-Based Photodiodes via Yttrium Oxide Coating and Decoating

Semiconducting single-walled carbon nanotube thin films can be obtained by conjugated polymer wrapping sorting technique followed by solution deposition and can be utilized as channel materials of field-effect transistors and absorbing layers of photodiodes. However, after the deposition process, there are still polymer molecules wrapping around nanotubes, remaining between nanotubes, and remaining on the thin-film surface, which will cause large nanotube-electrode resistance and tube-tube resistance. Here, we demonstrate an yttrium oxide coating-and-decoating technique that can remove polymers only around electrodes and thus improve the performance of photodiodes without inducing new defects in the device channel. After the treatment of only the contact area, the average short-circuit current of a photodiode increases from 9.1 to 10.7 nA, whereas the average open-circuit voltage increases from 0.25 to 0.30 V. This method also improves device uniformity significantly.

Carbon Nanotube Complementary Gigahertz Integrated Circuits and Their Applications on Wireless Sensor Interface Systems

Along with ultralow-energy delay products and symmetric complementary polarities, carbon nanotube field-effect transistors (CNT FETs) are expected to be promising building blocks for energy-efficient computing technology. However, the work frequencies of the existing CNT-based complementary metal-oxide-semiconductor (CMOS) integrated circuits (ICs) are far below the requirement (850 MHz) in state-of-art wireless communication applications. In this work, we fabricated deep submicron CMOS FETs with considerably improved performance of n-type CNT FETs and hence significantly promoted the work frequency of CNT CMOS ICs to 1.98 GHz. Based on these high-speed and sensitive voltage-controlled oscillators, we then presented a wireless sensor interface circuit with working frequency up to 1.5 GHz spectrum. As a preliminary demonstration, an energy-efficient wireless temperature sensing interface system was realized combining a 150 mAh flexible Li-ion battery and a flexible antenna (center frequency of 915 MHz). In general, the CMOS-logic high-speed CNT ICs showed outstanding energy efficiency and thus may potentially advance the application of CNT-based electronics.

Low Residual Carrier Concentration and High Mobility in 2D Semiconducting Bi2O2Se

The air-stable and high-mobility two-dimensional (2D) Bi₂O₂Se semiconductor has emerged as a promising alternative that is complementary to graphene, MoS₂, and black phosphorus for next-generation digital applications. However, the room-temperature residual charge carrier concentration of 2D Bi₂O₂Se nanoplates synthesized so far is as high as about 10¹⁹-10²⁰ cm^-3, which results in a poor electrostatic gate control and unsuitable threshold voltage, detrimental to the fabrication of high-performance low-power devices. Here, we first present a facile approach for synthesizing 2D Bi₂O₂Se single crystals with ultralow carrier concentration of ∼10¹⁶ cm^-3 and high Hall mobility up to 410 cm² V^-1 s^-1 simultaneously at room temperature. With optimized conditions, these high-mobility and low-carrier-concentration 2D Bi₂O₂Se nanoplates with domain sizes greater than 250 μm and thicknesses down to 4 layers (∼2.5 nm) were readily grown by using Se and Bi₂O₃ powders as coevaporation sources in a dual heating zone chemical vapor deposition (CVD) system. High-quality 2D Bi₂O₂Se crystals were fabricated into high-performance and low-power transistors, showing excellent current modulation of >10⁶, robust current saturation, and low threshold voltage of -0.4 V. All these features suggest 2D Bi₂O₂Se as an alternative option for high-performance low-power digital applications.

Wafer-Scale Fabrication of Ultrathin Flexible Electronic Systems via Capillary-Assisted Electrochemical Delamination

Electronic systems on ultrathin polymer films are generally processed with rigid supporting substrates during fabrication, followed by delamination and transfer to the targeted working areas. The challenge associated with an efficient and innocuous delamination operation is one of the major hurdles toward high-performance ultrathin flexible electronics at large scale. Herein, a facile, rapid, damage-free approach is reported for detachment of wafer-scale ultrathin electronic foils from Si wafers by capillary-assisted electrochemical delamination (CAED). Anodic etching and capillary action drive an electrolyte solution to penetrate and split the polymer/Si interface, leading to complete peel-off of the electronic foil with a 100% success rate. The delamination speed can be controlled by the applied voltage and salt concentration, reaching a maximum value of 1.66 mm s^-1 at 20 V using 2 m NaCl solution. Such a process incurs neither mechanical damage nor chemical contamination; therefore, the delaminated electronic systems remain intact, as demonstrated by high-performance carbon nanotube (CNT)-based thin-film transistors and integrated circuits constructed on a 5.5 cm × 5.0 cm parylene-based film with 4 µm thickness. Furthermore, the CAED strategy can be applied for prevalent polymer films and confers great flexibility and capability for designing and manufacturing diverse ultrathin electronic systems.

Interlayer electrical resistivity of rotated graphene layers studied by in-situ scanning electron microscopy

Interlayer electrical transport between two-dimensional atomic crystals can be strongly modulated by the rotational misalignment between them. However, the experimental study on the interlayer electrical transport between rotated two-dimensional atomic crystals with variable rotation angles is challenging. Here, an in-situ scanning electron microscopy method is developed to study the interlayer electrical transport between rotated graphene layers. We employ nanoprobes installed in a scanning electron microscope to function as both "fingers" to induce interlayer rotation of a microfabricated metal-graphite-metal sandwiched island and also electrical probes to measure interlayer electrical resistivity of the rotated graphene layers. Interlayer electrical resistivity of the rotated graphene layers is found to increase monotonically by three orders of magnitude from ∼0.1 to ∼100 Ω cm when the rotational misalignment angle increases from 0° to 30°. This phenomenon can be well described by phonon-mediated electrical transport model. The large-magnitude tunability of interlayer electrical resistivity by mechanical rotation implies the potential applications of rotated graphene layers in nanoelectromechanical systems. Our results also provide a method for studying and tuning interlayer electrical transport between rotated two-dimensional atomic crystals.

Dirac-source field-effect transistors as energy-efficient, high-performance electronic switches

An efficient way to reduce the power consumption of electronic devices is to lower the supply voltage, but this voltage is restricted by the thermionic limit of subthreshold swing (SS), 60 millivolts per decade, in field-effect transistors (FETs). We show that a graphene Dirac source (DS) with a much narrower electron density distribution around the Fermi level than that of conventional FETs can lower SS. A DS-FET with a carbon nanotube channel provided an average SS of 40 millivolts per decade over four decades of current at room temperature and high device current I60 of up to 40 microamperes per micrometer at 60 millivolts per decade. When compared with state-of-the-art silicon 14-nanometer node FETs, a similar on-state current Ion is realized but at a much lower supply voltage of 0.5 volts (versus 0.7 volts for silicon) and a much steeper SS below 35 millivolts per decade in the off-state.

Aligning Solution-Derived Carbon Nanotube Film with Full Surface Coverage for High-Performance Electronics Applications

The main challenge for application of solution-derived carbon nanotubes (CNTs) in high performance field-effect transistor (FET) is how to align CNTs into an array with high density and full surface coverage. A directional shrinking transfer method is developed to realize high density aligned array based on randomly orientated CNT network film. Through transferring a solution-derived CNT network film onto a stretched retractable film followed by a shrinking process, alignment degree and density of CNT film increase with the shrinking multiple. The quadruply shrunk CNT films present well alignment, which is identified by the polarized Raman spectroscopy and electrical transport measurements. Based on the high quality and high density aligned CNT array, the fabricated FETs with channel length of 300 nm present ultrahigh performance including on-state current I_on of 290 µA µm^-1 (V_ds = -1.5 V and V_gs = -2 V) and peak transconductance g_m of 150 µS µm^-1 , which are, respectively, among the highest corresponding values in the reported CNT array FETs. High quality and high semiconducting purity CNT arrays with high density and full coverage obtained through this method promote the development of high performance CNT-based electronics.

High-Performance Carbon Nanotube Complementary Electronics and Integrated Sensor Systems on Ultrathin Plastic Foil

The longtime vacancy of high-performance complementary metal-oxide-semiconductor (CMOS) technology on plastics is a non-negligible obstacle to the applications of flexible electronics with advanced functions, such as continuous health monitoring with in situ signal processing and wireless communication capabilities, in which high speed, low power consumption, and complex functionality are desired for integrated circuits (ICs). Here, we report the implementation of carbon nanotube (CNT)-based high-performance CMOS technology and its application for signal processing in an integrated sensor system for human body monitoring on ultrathin plastic foil with a thickness of 2.5 μm. The performances of both the p- and n-type CNT field-effect transistors (FETs) are excellent and symmetric on plastic foil with a low operation voltage of 2 V: width-normalized transconductances ( g_m/ W) as high as 4.69 μS/μm and 5.45 μS/μm, width-normalized on-state currents reaching 5.85 μA/μm and 6.05 μA/μm, and mobilities up to 80.26 cm²·V^-1·s^-1 and 97.09 cm²·V^-1·s^-1, respectively, together with a current on/off ratio of approximately 10⁵. The devices were mechanically robust, withstanding a curvature radius down to 124 μm. Utilizing these transistors, various high-performance CMOS digital ICs with rail-to-rail output and a ring oscillator on plastics with an oscillation frequency of 5 MHz were demonstrated. Furthermore, an ultrathin skin-mounted humidity sensor system with in situ frequency modulation signal processing capability was realized to monitor human body sweating.

Scalable Preparation of High-Density Semiconducting Carbon Nanotube Arrays for High-Performance Field-Effect Transistors

Although chemical vapor deposition (CVD)-grown carbon nanotube (CNT) arrays are considered ideal materials for constructing high-performance field-effect transistors (FETs) and integrated circuits (ICs), a significant gap remains between the required and achieved densities and purities of CNT arrays. Here, we develop a directional shrinking transfer method to realize up to 10-fold density amplification of CNT array films without introducing detectable damage or defects. In addition, the method improves the film uniformity while retaining the perfect alignment and high carrier mobility of 1600 cm² V^-1 s^-1 of CVD-grown CNT arrays. By combining the density amplification method with the thermocapillary flow method developed by Rogers et al., semiconducting CNT arrays with high densities and high qualities are obtained. High-performance FETs with a channel length of 200 nm are demonstrated using these high-density semiconducting CNT arrays, yielding a record-high on-state current density of 150 μA/μm, a peak transconductance of 80 μS/μm, and a current on/off ratio of more than 10⁴ among the CVD-grown CNT-based FETs.

Atomic-Layer-Deposition Growth of an Ultrathin HfO2 Film on Graphene

Direct growth of an ultrathin gate dielectric layer with high uniformity and high quality on graphene remains a challenge for developing graphene-based transistors due to the chemically inert surface properties of graphene. Here, we develop a method to realize atomic-layer-deposition (ALD) growth of an ultrathin high-κ dielectric layer on graphene through premodifying the graphene surface using electron beam irradiation. An amorphous carbon layer induced by electron beam scanning is formed on graphene and then acts as seeds for ALD growth of high-κ dielectrics. A uniform HfO₂ layer with an equivalent oxide thickness of 1.3 nm was grown as a gate dielectric for top-gate graphene field-effect transistors (FETs). The achieved gate capacitance is up to 2.63 μF/cm², which is the highest gate capacitance on a graphene solid-state device to date. In addition, the fabricated top-gate graphene FETs present a high carrier mobility of up to 2500 cm²/(V·s) and a negligible gate leakage current of down to 0.1 mA/cm², showing that the ALD-grown HfO₂ dielectric layer is highly uniform and of very high quality.

Electrically driven monolithic subwavelength plasmonic interconnect circuits

In the post-Moore era, an electrically driven monolithic optoelectronic integrated circuit (OEIC) fabricated from a single material is pursued globally to enable the construction of wafer-scale compact computing systems with powerful processing capabilities and low-power consumption. We report a monolithic plasmonic interconnect circuit (PIC) consisting of a photovoltaic (PV) cascading detector, Au-strip waveguides, and electrically driven surface plasmon polariton (SPP) sources. These components are fabricated from carbon nanotubes (CNTs) via a CMOS (complementary metal-oxide semiconductor)-compatible doping-free technique in the same feature size, which can be reduced to deep-subwavelength scale (~λ/7 to λ/95, λ = 1340 nm) compared with the 14-nm technique node. An OEIC could potentially be configured as a repeater for data transport because of its "photovoltaic" operation mode to transform SPP energy directly into electricity to drive subsequent electronic circuits. Moreover, chip-scale throughput capability has also been demonstrated by fabricating a 20 × 20 PIC array on a 10 mm × 10 mm wafer. Tailoring photonics for monolithic integration with electronics beyond the diffraction limit opens a new era of chip-level nanoscale electronic-photonic systems, introducing a new path to innovate toward much faster, smaller, and cheaper computing frameworks.

Scaling down contact length in complementary carbon nanotube field-effect transistors

We performed an experimental investigation on contact length (L_c) scaling of carbon nanotube (CNT) complementary field-effect transistors (FETs). Contact resistances of Sc-contacted (for n-type) and Pd-contacted (for p-type) CNT FETs are respectively retrieved based on the experimental data through the transfer length method (TLM). The performance of L_c scaling of Sc/CNT is proved to be comparable to that of the Pd/CNT contact with L_c larger than approximately 40 nm, but it degrades sharply when further scaling down L_c mainly owing to the surface oxidation of the Sc film. After decoupling the effect of oxide thickness, the intrinsic contact scaling behavior of Sc-contacted CNT FETs is found to be as good as that of the Pd-contacted ones, which can further satisfy the requirement of developing complementary CNT FET technology scaled down to the 14 nm node.

Carbon nanotube-based three-dimensional monolithic optoelectronic integrated system

Single material-based monolithic optoelectronic integration with complementary metal oxide semiconductor-compatible signal processing circuits is one of the most pursued approaches in the post-Moore era to realize rapid data communication and functional diversification in a limited three-dimensional space. Here, we report an electrically driven carbon nanotube-based on-chip three-dimensional optoelectronic integrated circuit. We demonstrate that photovoltaic receivers, electrically driven transmitters and on-chip electronic circuits can all be fabricated using carbon nanotubes via a complementary metal oxide semiconductor-compatible low-temperature process, providing a seamless integration platform for realizing monolithic three-dimensional optoelectronic integrated circuits with diversified functionality such as the heterogeneous AND gates. These circuits can be vertically scaled down to sub-30 nm and operates in photovoltaic mode at room temperature. Parallel optical communication between functional layers, for example, bottom-layer digital circuits and top-layer memory, has been demonstrated by mapping data using a 2 × 2 transmitter/receiver array, which could be extended as the next generation energy-efficient signal processing paradigm.

Single-material monolithic optoelectronic integrated circuits via CMOS compatible low-temperature approaches are crucial to the continued development of post-Moore electronics. Liu et al., report carbon nanotube based electrically driven 3D monolithic optoelectronic integrated circuits.

Carbon nanotube radio-frequency electronics

Carbon nanotube (CNT) is considered a promising material for radio-frequency (RF) applications, owing to its high carrier mobility and saturated drift velocity, as well as ultra-small intrinsic gate capacitance. Here, we review progress on CNT-based devices and integrated circuits for RF applications, including theoretical projection of RF performance of CNT-based devices, preparation of CNT materials, fabrication, optimization of RF field-effect transistors (FETs) structures, and ambipolar FET-based RF applications, and we outline challenges and prospects of CNT-based RF applications.

High-Performance Complementary Transistors and Medium-Scale Integrated Circuits Based on Carbon Nanotube Thin Films

Solution-derived carbon nanotube (CNT) network films with high semiconducting purity are suitable materials for the wafer-scale fabrication of field-effect transistors (FETs) and integrated circuits (ICs). However, it is challenging to realize high-performance complementary metal-oxide semiconductor (CMOS) FETs with high yield and stability on such CNT network films, and this difficulty hinders the development of CNT-film-based ICs. In this work, we developed a doping-free process for the fabrication of CMOS FETs based on solution-processed CNT network films, in which the polarity of the FETs was controlled using Sc or Pd as the source/drain contacts to selectively inject carriers into the channels. The fabricated top-gated CMOS FETs showed high symmetry between the characteristics of n- and p-type devices and exhibited high-performance uniformity and excellent scalability down to a gate length of 1 μm. Many common types of CMOS ICs, including typical logic gates, sequential circuits, and arithmetic units, were constructed based on CNT films, and the fabricated ICs exhibited rail-to-rail outputs because of the high noise margin of CMOS circuits. In particular, 4-bit full adders consisting of 132 CMOS FETs were realized with 100% yield, thereby demonstrating that this CMOS technology shows the potential to advance the development of medium-scale CNT-network-film-based ICs.

Plasmonic Enhanced Performance of an Infrared Detector Based on Carbon Nanotube Films

The carbon nanotube (CNT) has been proved to be a promising material in infrared detection, due to its many advantages of high mobility, strong infrared light absorption, and carrier collection efficiency. However, the absorption restriction from the single layer limits its effective utilization of incident light. In this paper, we introduce a plasmonic electrode structure in a CNT thin-film photodetector based on random deposited high-purity semiconducting CNTs, which can collect photoinduced carriers effectively and enhance light absorption at the same time. The largest enhancement of photocurrents can be achieved at 1650 nm wavelength with suitable plasmonic structure size. Especially, we further discuss the influence of plasmonic structures on the performance of devices. We demonstrate that the best performance improvement of the carbon nanotube detector with plasmonic structure can be enhanced by 13.7 times for photocurrent mode and 5.62 times for photovoltage mode compared to those devices without structure at 1650 nm resonant wavelength. At last, the plasmonic structures are applied on tandem photodetectors with nine virtual contacts, and both the photocurrent and photovoltage are increased. The application of plasmonic electrodes can improve detector performance and retain compact device structures, which shows great potential for optimizing infrared detectors based on nanomaterials.

Water-Assisted Preparation of High-Purity Semiconducting (14,4) Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (s-SWNTs) with diameters of 1.0-1.5 nm (with similar bandgap to crystalline silicon) are highly desired for nanoelectronics. Up to date, the highest reported content of s-SWNTs as-grown is ∼97%, which is still far below the daunting requirements of high-end applications. Herein, we report a feasible and green pathway to use H₂O vapor to modulate the structure of the intermetallic W₆Co₇ nanocrystals. By using the resultant W₆Co₇ nanocatalysts with a high percentage of (1 0 10) planes as structural templates, we realized the direct growth of s-SWNT with the purity of ∼99%, in which ∼97% is (14,4) tubes (diameter 1.29 nm). H₂O can also act as an environmentally friendly and facile etchant for eliminating metallic SWNTs, and the content of s-SWNTs was further improved to 99.8% and (14,4) tubes to 98.6%. High purity s-SWNTs with even bandgap determined by their uniform structure can be used for the exquisite applications in different fields.

Asymmetric Light Excitation for Photodetectors Based on Nanoscale Semiconductors

A photodetector is a key device to extend the cognition fields of mankind and to enrich information transfer. With the advent of emerging nanomaterials and nanophotonic techniques, new explorations and designs for photodetection have been constantly put forward. Here, we report the asymmetric-light-excitation photoelectric detectors with symmetric electrical contacts working at zero external bias. Unlike conventional photodetectors with symmetric contacts which are usually used as photoconductors or phototransistors showing no photocurrent at zero bias, in this device, the asymmetric-light-excitation structure is designed to ensure that only one Schottky junction between two metallic electrodes and semiconductors is illuminated. In this condition, a device can contribute to a photocurrent without bias. Furthermore, incident light with global illumination will be redistributed by the top Au patterns on devices. The achievement of detectors benefits from the designed redistribution of optical field on specific Schottky barriers within optically active regions and effective carrier collection, producing unidirectional photocurrent for large-scale detection applications. The response mechanisms, including excitations under different polarizations, wavebands, and tilted incidences, were systematically elaborated. Device performances including photocurrent, dynamic response, and detectivity were also carefully measured, demonstrating the possibility for applications in high-speed imaging sensors or integrated optoelectronic systems. The concept of asymmetric-light-excitation photodetectors shows wider availability to other nanomaterials for modern optoelectronics.

Sensitivity enhancement of graphene Hall sensors modified by single-molecule magnets at room temperature

Sensitivity of graphene Hall sensors was enhanced by modifying single-molecule magnets with excellent linearity, off voltage, repeatability and stability.

Machine-Washable Textile Triboelectric Nanogenerators for Effective Human Respiratory Monitoring through Loom Weaving of Metallic Yarns

Textile triboelectric nanogenerators for human respiratory monitoring with machine washability are developed through loom weaving of Cu-PET and PI-Cu-PET yarns. Triboelectric charges are generated at the yarn crisscross intersections to achieve a maximum short circuit current density of 15.50 mA m^-2 . By integrating into a chest strap, human respiratory rate and depth can be monitored.

High Conversion Efficiency Carbon Nanotube-Based Barrier-Free Bipolar-Diode Photodetector

Conversion efficiency (CE) is the most important figure of merit for photodetectors. For carbon nanotubes (CNT) based photodetectors, the CE is mainly determined by excitons dissociation and transport of free carriers toward contacts. While phonon-assisted exciton dissociation mechanism is effective in split-gate CNT p-n diodes, the CE is typically low in these devices, approximately 1-5%. Here, we evaluate the performance of a barrier-free bipolar diode (BFBD), which is basically a semiconducting CNT asymmetrically contacted by perfect n-type ohmic contact (Sc) and p-type ohmic contact (Pd) at the two ends of the diode. We show that the CE in short channel BFBD devices (e.g., 60 nm) is over 60%, and it reduces rapidly with increasing channel length. We find that the electric-field-assisted mechanism dominates the dissociation rate of excitons in BFBD devices at zero bias and thus the photocurrent generation process. By performing a time-resolved and spatial-resolved Monte Carlo simulation, we find that there exists an effective electron (hole)-rich region near the n-type (p-type) electrode in the asymmetrically contacted BFBD device, where the electric-field strength is larger than 17 V/μm and exciton dissociation is extremely fast (<0.1 ps), leading to very high CE in the BFBD devices.

Contact-dominated transport in carbon nanotube thin films: toward large-scale fabrication of high performance photovoltaic devices

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been widely regarded as potential channel materials for not only replacing silicon to extend Moore's law but also for building high performance optoelectronic devices. To realize these goals, high quality s-SWCNTs and contacts are needed to outperform devices based on traditional materials such as silicon. For a high quality conducting or active channel, the ideal CNTs consist of a pure s-SWCNTs array with a confined pitch of less than 10 nm via e.g., chemical vapor deposition (CVD) methods, although this has not been realized experimentally. On the other hand, significant progress has been made on solution-processed CNTs. However, only network and low performance optoelectronic devices have been realized. In this study, we systematically studied the performance of devices using solution-processed CNT films with different s-SWCNT purity, with particular emphasis being placed on disentangling those metallic-CNTs (m-CNTs)-dominated low performance and contacts-dominated high performance devices. We demonstrated that using high purity s-SWCNTs allowed for the construction of high performance diodes via a doping-free method. These diodes behave similarly to those based on individual CVD-grown s-CNTs, resulting in 250 mV photovoltage for a typical single diode and more than 4.35 V for cascading cells using the virtual contact technique and thus paving the way for large scale fabrication of higher performance photovoltaic devices using readily available solution processed CNTs.