High-performance Electronics Research Articles

Elastic polyaniline nanoarrays/MXene textiles for all-solid-state supercapacitors and anisotropic strain sensors

Wearable electronics have attracted much attention in recent years, and textiles have been considered as the desirable substrate. However, it remains a critical challenge to fabricate electronic textiles that are multifunctional, breathable, highly conductive, and elastic. Herein, we develop a novel chemical polymerization and coating strategy to construct interconnected networks of polyaniline (PANI) nanoarrays and MXene on the fiber surface. The fabricated PANI nanoarrays/MXene modified rib knitting fabric exhibit low electrical resistance and good elasticity. The all-solid-state PANI/MXene fabric-based supercapacitors show a high specific capacitance and energy density of 647 mF/cm2 and 8.08 μWh/cm2, respectively, which is higher than most MXene-based textiles. Moreover, the PANI/MXene fabrics demonstrate anisotropic yet exceptional strain sensing performance, including high sensitivity (gauge factor, 435.0), linearity (>0.9), and wide range (0–40.8%), which enables them as wearable sensors to detect large human motions accurately. This work provides a new approach to accomplishing high-performance textile-based wearable electronics.

Hydrogen-Terminated Diamond MOSFETs Using Ultrathin Glassy Ga2O3 Dielectric Formed by Low-Temperature Liquid Metal Printing Method

The p-type surface conductivity of hydrogen-terminated diamond (H-diamond) provides a viable approach toward diamond-based wide-bandgap metal-oxide-semiconductor field-effect transistors (MOSFETs) for high-power and high-frequency electronics. A facile, low-cost, and low-temperature method to form gate dielectrics on diamond that also preserves the integrity of hydrogen-termination is highly desirable for high-performance diamond surface electronics with process flexibility and high yield. In this work, we demonstrate a p-channel diamond MOSFET with an ultrathin glassy Ga2O3 dielectric layer derived from liquid metal. A liquid metal printing method was employed to transfer an amorphous Ga2O3 layer over the desired active p-channel region of H-diamond at low temperature, allowing the protection and preservation the hydrogen-terminated surface while also forming an efficient gate dielectric. The results of this work suggest that the liquid metal method can provide an efficient, low-cost, and high-yield pathway to form high-quality dielectrics for diamond-based transistors.

Improving field emission performance of patterned ZnO electron emission source by optimizing array spacing

The field emission (FE) electron source has a wide range of application in the field of vacuum electronics, and the patterning of cathode emitters is one of the key technology. In this paper, a new idea of cathode structure to achieve good luminescence uniformity with the smallest emitter areas is proposed. First, the inkjet printing is applied to precisely position the patterned layer, and the branched ZnO arrays are grown by electrochemical deposition. Then the effect of array spacings on field emission performance is studied. The results show that with the increase of the array spacing, the FE performance first increases and then decreases, among which the arrays with the moderate spacing have the best FE properties, including the lowest turn-on field (Eon) of ∼0.46 V μm−1 and the most uniform luminescence. Finite element calculations using the ANSYS software were performed. Simulations are carried out to analyze the surface electric field distribution and electron movement trajectory, indicating the moderate array spacing is beneficial for FE due to the balance of the field superposition effect and shielding effect. The efficiency of pattern design helps to realize the high-performance field emission electron source, which is of great significance for flexible manufacturing and large-scale integration.

Strain-Free Layered Semiconductors for 2D Transistors with On-State Current Density Exceeding 1.3 mA μm-1.

High-mobility and air-stable two-dimensional (2D) Bi2O2Se semiconductor holds promise as an alternative fast channel material for next-generation transistors. However, one of the key challenges remaining in 2D Bi2O2Se is to prepare high-quality crystals to fabricate the high-performance transistors with a high on-state current density. Here, we present the free-standing growth of strain-free 2D Bi2O2Se crystals. An ultrahigh Hall mobility of 160 000 cm2 V-1 s-1 is measured in strain-free Bi2O2Se crystals at 2 K, which enables the observation of Shubnikov-de Haas quantum oscillations and shows substantially higher (>4 times) mobility over previous in-plane 2D crystals. The fabricated 2D transistors feature an on-off current ratio of ∼106 and a record-high on-state current density of ∼1.33 mA μm-1, which is comparable to that of commercial Si and Ge n-type field-effect transistors (FETs) for similar channel length. Strain-free 2D Bi2O2Se provides a promising material platform for studying novel quantum phenomena and exploration of high-performance low-power electronics.

Analysis of Low-Frequency 1/f Noise Characteristics for MoTe2 Ambipolar Field-Effect Transistors.

Low-frequency electronic noise is an important parameter used for the electronic and sensing applications of transistors. Here, we performed a systematic study on the low-frequency noise mechanism for both p-channel and n-channel MoTe2 field-effect transistors (FET) at different temperatures, finding that low-frequency noise for both p-type and n-type conduction in MoTe2 devices come from the variable range hopping (VRH) transport process where carrier number fluctuations (CNF) occur. This process results in the broad distribution of the waiting time of the carriers between successive hops, causing the noise to increase as the temperature decreases. Moreover, we found the noise magnitude for p-type MoTe2 FET hardly changed after exposure to the ambient conditions, whereas for n-FET, the magnitude increased by nearly one order. These noise characteristics may provide useful guidelines for developing high-performance electronics based on the emerging transition metal dichalcogenides.

A Highly Conducting Polymer for Self-Healable, Printable, and Stretchable Organic Electrochemical Transistor Arrays and Near Hysteresis-Free Soft Tactile Sensors.

A stretchable and self-healable conductive material with high conductivity is critical to high-performance wearable electronics and integrated devices for applications where large mechanical deformation is involved. While there has been great progress in developing stretchable and self-healable conducting materials, it remains challenging to concurrently maintain and recover such functionalities before and after healing. Here, a highly stretchable and autonomic self-healable conducting film consisting of a conducting polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) and a soft-polymer (poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PAAMPSA) is reported. The optimal film exhibits outstanding stretchability as high as 630% and high electrical conductivity of 320 S cm-1 , while possessing the ability to repair both mechanical and electrical breakdowns when undergoing severe damage at ambient conditions. This polymer composite film is further utilized in a tactile sensor, which exhibits good pressure sensitivity of 164.5 kPa-1 , near hysteresis-free, an ultrafast response time of 19ms, and excellent endurance over 1500 consecutive presses. Additionally, an integrated 5 × 4 stretchable and self-healable organic electrochemical transistor (OECT) array with great device performance is successfully demonstrated. The developed stretchable and autonomic self-healable conducting film significantly increases the practicality and shelf life of wearable electronics, which in turn, reduces maintenance costs and build-up of electronic waste.

Non-simultaneous droplet impingement cooling of a solid heated surface

High generation of heat in the electronics industry presents a roadblock for further innovations in higher processing power due to complications associated with overheating. Commonly used air-based systems cannot cool high-performance electronics, mainly due to the relatively poor thermo-physical properties of air. Spray cooling is a technique capable of cooling or quenching objects at very high temperatures and heat fluxes. While there has been considerable research on single droplet impact to study the fundamentals of spray cooling, multiple droplet impingement offers more realistic realisations of the dynamics of spray phenomena. In this paper, we examined the fluid dynamics and heat transfer of multiple droplet impingement using high-speed imaging and fast heat flux measurements to capture droplet-droplet and droplet-surface interactions at constant droplet Weber number. We investigated an individual droplet and two non-simultaneous droplets of water at a constant horizontal droplet spacing and different time separations to analyse the heat transfer at different initial surface temperatures. Although not affected significantly by the surface temperature, the maximum diameter of the combined droplets decreased for increasing time separation due to the kinematic discontinuity from the interaction between droplets moving in opposite direction. For small time separation, the spreading droplet contact line of the first droplet collided with the moving contact line of the second droplet. The receding and the quasi-static contact lines of the first droplet was strongly and mildly impacted by the second spreading droplet diameter, respectively. However, all quasi-static droplet diameters increased for non-simultaneous droplet scenario, following by a small reduction in the droplet diameter when the surface temperature increased due to evaporation. Depending on the surface temperature and time separation between droplets, it was found that the peak heat transfer rates for non-simultaneous droplet impingement scenarios can be increased by 68% to 100% when compared to a single droplet case due to higher combined droplet diameter and fluid volume in contact with the heated solid surface. However, the overall droplet cooling efficiency was higher for the single droplet case, showing that the droplet-droplet interaction can decrease the potential cooling performance of droplets. The present study provides knowledge combining droplet-droplet interaction and heat transfer performance for future spray cooling system design and optimisation.

Towards the synthesis of semiconducting single-walled carbon nanotubes by floating-catalyst chemical vapor deposition: Challenges of reproducibility

High-purity semiconducting single-walled carbon nanotubes (s-SWCNTs) are of paramount significance for the fabrication of high-performance electronics. Here, we present continuous production of high-purity, long, and isolated s-SWCNTs by gas-phase synthesis, retaining the pristine morphologies of as-synthesized nanotubes. The s-SWCNTs were synthesized at ca. 920 °C using ethanol and methanol as carbon source and growth enhancer, respectively in N2 and H2. The purity of as-produced s-SWCNTs with a mean length of 15.2 μm can reach 98% as determined by optical absorption spectroscopy. We observed that the overpressure in the reactor and methanol are the principal causes of the enrichment of s-SWCNTs. Specifically, the s-SWCNTs were found to be more negatively charged, and oxygen-contained species play critical roles in the s-SWCNT synthesis. Through the demonstration of field-effect transistors, the s-SWCNTs exhibit a high mean charge carrier mobility of 453.3 cm2 V−1 s−1 which is 2.27 times higher than that of the transistors fabricated with high-quality dispersion-processed SWCNTs. Additionally, we discuss the challenges of synthesis repeatability and recommend a few tips to improve reproducibility. Our study represents an important step towards the scalable production of clean, long, and isolated s-SWCNTs with high purity and narrow bandgap distribution.

Attributes of High-Performance Electron Transport Layers for Perovskite Solar Cells on Flexible PET versus on Glass.

Electron transport layers (ETLs) play a fundamental role in perovskite solar cells (PSCs) through charge extraction. Here, we developed flexible PSCs on 12 different kinds of ETLs based on SnO2. We show that ETLs need to be specifically developed for plastic substrates in order to attain 15% efficient flexible cells. Recipes developed for glass substrates do not typically transfer directly. Among all the ETLs, ZnO/SnO2 double layers delivered the highest average power conversion efficiency of 14.6% (best cell 14.8%), 39% higher than that of flexible cells of the same batch based on SnO2-only ETLs. However, the cells with a single ETL made of SnO2 nanoparticles were found to be more stable as well as more efficient and reproducible than SnO2 formed from a liquid precursor (SnO2-LP). We aimed at increasing the understanding of what makes a good ETL on polyethylene terephthalate (PET) substrates. More so than ensuring electron transport (as seen from on-current and series resistance analysis), delivering high shunt resistances (RSH) and lower recombination currents (Ioff) is key to obtain high efficiency. In fact, RSH of PSCs fabricated on glass was twice as large, and Ioff was 76% lower in relative terms, on average, than those on PET, indicating considerably better blocking behavior of ETLs on glass, which to a large extent explains the differences in average PCE (+29% in relative terms for glass vs PET) between these two types of devices. Importantly, we also found a clear trend for all ETLs and for different substrates between the wetting behavior of each surface and the final performance of the device, with efficiencies increasing with lower contact angles (ranging between ∼50 and 80°). Better wetting, with average contact angles being lower by 25% on glass versus PET, was conducive to delivering higher-quality layers and interfaces. This cognizance can help further optimize flexible devices and close the efficiency gap that still exists with their glass counterparts.

Developing compact and high performance electron sources with silicon carbide

Sources with a sub-micron beam and 10 to 20 electrons per shot explore new application space

Hybrid Integration of Screen-Printed RFID Tags and Rigid Microchip on Paper

Hybrid or heterogeneous integration of silicon technologies and printed electronics is a promising approach for high-performance flexible electronics. It is essentially the integration of rigid microchips with the printed circuit on a flexible substrate. However, microchips with no-lead and millimeter-size pitch introduce practical challenges in terms of precise electrical bonding onto the printed pattern. The differences in mechanical and thermal requirements also make it challenging to use conventional bonding and interconnect technology to robustly connect the microchips on flexible substrates. The focus of this work is to present these challenges with respect to different substrate–adhesive combinations and to provide a facile technique for integrating near-field communication (NFC) microchips on different flexible substrates. Following the successful integration, the smart tags were characterized to demonstrate reliable performance in the NFC reading range. While presenting a hybrid integration for the smart tag, this work also shows a potential solution for several other applications of flexible electronics where high performance cannot be achieved by printed electronics alone.

A New Noncovalently Fused-Ring Electron Acceptor Based on 3,7-Dialkyloxybenzo[1,2-b:4,5-b']dithiophene for Low-Cost and High-Performance Organic Solar Cells.

The innovation of high-performance fused-ring electron acceptors (FREAs) has carried the field of organic solar cells (OSCs) toward a new stage of development. However, due to high synthetic complexity and production costs, FREAs may not be the most promising candidates for future commercialization applications. To address these disadvantages of FREAs, a series of low-cost acceptors, named as noncovalently FREAs (NFREAs), is successfully constructed by employing the strategy of noncovalently conformational locks. Herein, a novel NFREA (BDTO-4F) based on 3,7-dialkyloxybenzo[1,2-b:4,5-b']dithiophene is synthesized and fully characterized. Benefiting from the complementary absorption of the donor and acceptor, balanced charge transport, and favorable film morphology, J52:BDTO-4F based OSCs afford a satisfied power conversion efficiency of 12.09%, much higher than PBDB-T:BDTO-4F-based devices (8.30%). It is worth mentioning that BDTO-4F possesses a higher figure-of-merit value of 55.65 in comparison with several representative FREAs based on a cost-efficiency evaluation. This work demonstrates the potential of the novel benzo[1,2-b:4,5-b″]dithiophene derivative for constructing low-cost and high-performance NFREAs, providing a valuable insight on the materials design.

Combining one and two photon polymerization for accelerated high performance (3 + 1)D photonic integration

Abstract Dense and efficient circuits with component sizes approaching the physical limit is the hallmark of high performance integration. Ultimately, these features and their pursuit enabled the multi-decade lasting exponential increase of components on integrated electronic chips according to Moore’s law, which culminated with the high performance electronics we know today. However, current fabrication technology is mostly constrained to 2D lithography, and thermal energy dissipation induced by switching electronic signal lines presents a fundamental challenge for truly 3D electronic integration. Photonics reduces this problem, and 3D photonic integration is therefore a highly sought after technology that strongly gains in relevance due to the need for scalable application-specific integrated circuits for neural networks. Direct laser writing of a photoresin is a promising high-resolution and complementary metal-oxide-semiconductor (CMOS) compatible tool for 3D photonic integration. Here, we combine one and two-photon polymerization (TPP) for waveguide integration for the first time, dramatically accelerating the fabrication process and increasing optical confinement. 3D additive printing is based on femtosecond TPP, while blanket irradiation with a UV lamp induces one-photon polymerization (OPP) throughout the entire 3D chip. We locally and dynamically adjust writing conditions to implement (3 + 1)D flash-TPP: waveguide cores are printed with a small distance between neighboring writing voxels to ensure smooth interfaces, mechanical support structures are printed at maximal distance between the voxels to speed up the process. Finally, the entire chip’s passive volume not part of waveguide cores or mechanical support is polymerized in a single instance by UV blanket irradiation. This decouples fabrication time from the passive volume’s size. We succeed in printing vertical single-mode waveguides of 6 mm length that reach numerical apertures up to NA = 0.16. Noteworthy, we achieve exceptionally low −0.26 dB injection losses and very low propagation losses of −1.36 dB/mm at λ 0 = 660 nm, which is within one order of magnitude of standard integrated silicon photonics. Finally, the optical performance of our waveguides does not deteriorate for at least ∼3000 h after printing, and remains stable during ∼600 h of continuous operation with 0.25 mW injected light.

Ultrafast electron diffraction apparatus at kiloelectron-volt energies

Generating high-performance pulsed electron beams using novel photocathodes

Highly reliable anisotropic interconnection system fabricated using Cu/Sn-Soldered microdumbbell arrays and polyimide films for application to flexible electronics

To fabricate high-performance flexible electronics, high-density electronic components should be safely integrated into limited areas, even under device deformation. However, simultaneously achieving device flexibility and strong bonds is challenging. Therefore, we fabricated Cu–Sn microdumbbell arrays on perforated polyimide (PI) substrates to develop a flexible interconnection system simultaneously exhibiting strong bonds and device flexibility by combining flexible PI films and metal–metal soldering. Cu microdumbbell arrays were formed by electroplating Cu on ∼5-μm-diameter microholes that were randomly distributed on flexible PI film surfaces and subsequently covering the dumbbell head surface with Sn by electroless plating. The Sn-covered dumbbell heads acted as metallic solder, enabling strong bonds with electronic components through hot pressing by forming nanolayered Cu/Sn intermetallic compounds. Electronic chips bonded by the Cu–Sn microdumbbell arrays exhibited excellent shear bonding strength, even after 10,000 bending cycles. Finite element simulations revealed that crack propagation was hindered by the space between the microdumbbells, thus enhancing the adhesion strength of the flexible interconnection system.

A modulus-engineered multi-layer polymer film with mechanical robustness for the application to highly deformable substrate platform in stretchable electronics

Mechanical robustness and deformability of substrate platforms are essential for high-performance stretchable electronics. However, there are still challenges because of rigid island design for device protecting that induces large modulus mismatch and impedes the out-of-plane deformation. Herein, a substrate platform with superb mechanical durability and deformability is newly devised by introducing a multi-layer polymer film (MLPF), where the modulus of each layer was engineered precisely range from 105 to 109 Pa. The modulus-engineered MLPF was integrated monolithically onto various elastomer substrates via sequential film deposition using initiated chemical vapor deposition (iCVD). The developed substrate platform exhibited outstanding robustness against various modes of deformations. Especially the tensile deformation, MLPF structure enhanced mechanical durability by 102 times than a single-layer island structure while keeping the strain on the island below 1 % even with the 99 % of global strain. The developed substrate platform was applied for amorphous Indium-Gallium-Zinc oxide TFT array. The TFT performances were maintained even under 30 % of tensile strain and they were fully retained after 105 times of repeated tensile deformation. The newly suggested substrate platform and design rule of MLPF structure will serve as a guideline for integration of future stretchable/wearable electronics achieving superb mechanical robustness and long-term operation.

High-Performance Carbon Nanotube-Based Transient Complementary Electronics.

Transient electronics is an emerging class of electronic devices that can physically degrade or disintegrate after a stable period of service, showing a vast prospect in applications of "green" consumer electronics, hardware-secure devices, medical implants, etc. Complementary metal-oxide-semiconductor (CMOS) technology is dominant in integrated circuit design for its advantages of low static power consumption, high noise immunity, and simple design layout, which also work and are highly preferred for transient electronics. However, the performance of complementary transient electronics is severely restricted by the confined selection of transient materials and compatible fabrication strategies. Here, we report the realization of high-performance transient complementary electronics based on carbon nanotube thin films via a reliable electrostatic doping method. Under a low operating voltage of 2 V, on a 1.5 μm-thick water-soluble substrate made of poly(vinyl alcohol), the width-normalized on-state currents of the p-type and n-type transient thin-film transistors (TFTs) reach 4.5 and 4.7 μA/μm, and the width-normalized transconductances reach 2.8 and 3.7 μS/μm, respectively. Meanwhile, these TFTs show small subthreshold swings no more than 108 mV/dec and current on/off ratios above 106 with good uniformity. Transient CMOS inverters, as basic circuit components, are demonstrated with a voltage gain of 24 and a high noise immunity of 67.4%. Finally, both the degradation of the active components and the disintegration of the functional system are continuously monitored with nontraceable remains after 10 and 5 h, respectively.

Comprehensive Study of the Resistance of Pencil-Stroked Graphite on Paper Electrodes

In this paper, we comprehensively study the electrical resistance of pencil-stroked graphite electrodes, which is a cheap electrical conductor. Thin graphite on paper (GOP) electrodes were manually fabricated by unidirectionally stroking rectangular areas defined by grids on graph paper, allowing the physical dimensions of the layer to be accurately represented. The physical dimensions of the electrode were then varied and the I–V relationship for the layer was characterized. Our findings indicate that these thin electrodes behave as ohmic conductors over the low voltage range (0–12 V), and their resistance can be quantitatively described by Pouillet’s Law [Formula: see text]. The deviation of the experimentally obtained linear I–V characteristic from the theoretical nonlinear I–V characteristic of graphite has been explained by measuring the temperature rise of the graphite electrode, which was found to be insignificant [Formula: see text] in the low voltage range. The effects of saturation level of the electrode and pencil grade on electrode resistance are also elaborated in this paper. By showing the turbostratic nature of graphite in GOP and analyzing its electronic conduction mechanism, the experimental observations have been explained theoretically. We also note the highly interesting low-energy electron dynamics in GOP reported previously in misoriented multilayer graphitic systems. We observed insignificant changes in electrode resistivity over five-minute intervals and repeated use. Hence, these electrodes exhibit great stability as a low-voltage electrical conductor. The flexibility, usability, and ease-of-synthesis of these thin graphite layers in large volumes, coupled with their remarkable electrical properties, present a novel approach for adopting them in designs of low-cost and high-performance sensors, foldable electronics, and microfluidics, paving the way for an electronics industry that can meet the stipulations of many more products.

High-performance heptacyclic ladder-type heteroarene-based electron acceptors enabled by bulky neighboring side-chains and end-group fluorination

A banana-shape heptacyclic heteroarene core without sp 3 -hybridized bridging atoms is designed and synthesized for constructing novel nonfullerene acceptors. Through introducing bulky neighboring side-chains and fluorinated terminals, molecular aggregation and crystallinity of the nonfullerene acceptors can be effectively modulated, thus leading to improved charge transport and device performance. • Non-fullerene acceptors with sp 3 -hybridized-carbon-free skeletons are developed. • Bulky neighboring side-chains leads to acceptors with suitable aggregation. • End-group fluorination leads to a 6-fold increase in the efficiency of acceptor. • An “A-to-D” type J -aggregation is observed for the acceptor. Although ladder-type heteroarene building blocks without sp 3 -hybridized bridging atoms have been widely used for the synthesis of polymer donors, they have rarely been applied for constructing non-fullerene acceptors (NFAs) mainly due to the lack of strategies to effectively modulate self-aggregation and crystallinity of the resulting acceptors. Herein, a novel sp 3 -hybridized-carbon-free ladder-type skeleton, benzo[2,1-b:3,4-b']bis(4H-dithieno[3,2-b:2′,3′-d]pyrrole) featuring with two sets of neighboring side-chains, is designed and successfully synthesized as a donor core for developing NFAs ( cis -MH and cis -MF). The single-crystal result shows that the cis -MF forms slip-stacked J -type aggregates and packs in an anti-parallel “face-to-face” manner due to the bulkiness effect of neighboring side-chains. This molecular stacking mode effectively prevents the formation of oversized aggregates in the corresponding active layer as evidenced by atomic force microscopy analyses. Introduction of the fluorinated terminals broadens the absorption range and increases the crystallinity of the acceptor, thus greatly promoting its carrier transport. As a result, the cis -MF-based device exhibits a 6-fold increase in power conversion efficiency compared to the cis -MH-based device. Overall, this work provides a new molecular design strategy as well as a novel sp 3 -hybridized-carbon-free ladder-type building block for developing efficient NFAs that can be used to further advance the PCEs of polymer solar cells.

Physics and applications of nanotubes

Nanotubes have been pursued aggressively over the last three decades. Significant progress has been made in the selective growth and post-synthetic sorting of highly monodisperse carbon nanotubes, in understanding their physics, and in assembling and integrating them into high-performance devices. These discoveries have led to promising applications in areas such as high-performance CMOS, high-speed RF, thin-film transistors, flexible electronics, thermoelectrics, sensors, and optoelectronics. The rapid development of modern information technology depends on the exploitation of new and novel materials, and nanotubes have emerged as promising candidates for the post-Moore's Law era. This Special Topic on Physics and Applications of Nanotubes provides a valuable forum where researchers studying the fundamentals of nanotubes can share their most recent and novel findings.