A high-yield two-step transfer printing method for large-scale fabrication of organic single-crystal devices on arbitrary substrates

A van der Waals Integrated Damage-Free Memristor Based on Layered 2D Hexagonal Boron Nitride

2D materials with intriguing properties have been widely used in optoelectronics. However, electronic devices suffered from structural damage due to the ultrathin materials and uncontrolled defects at interfaces upon metallization, which hindered the development of reliable devices. Here, a damage-free Au/h-BN/Au memristor is reported using a clean, water-assisted metal transfer approach by physically assembling Au electrodes onto the layered h-BN which minimized the structural damage and undesired interfacial defects. The memristors demonstrate significantly improved performance with the coexistence of nonpolar and threshold switching as well as tunable current levels by controlling the compliance current, compared with devices with evaporated contacts. The devices integrated into an array show suppressed sneak path current and can work as both logic gates and latches to implement logic operations allowing in-memory computing. Cross-sectional scanning transmission electron microscopy analysis validates the feasibility of this nondestructive metal integration approach, the crucial role of high-quality atomically sharp interface in resistive switching, and a direct observation of percolation path. The underlying mechanism of boron vacancies-assisted transport is further supported experimentally by conductive atomic force microscopy free from process-induced damage, and theoretically by ab initio simulations.

Ultralow-voltage all-carbon low-dimensional-material flexible transistors integrated by room-temperature photolithography incorporated filtration

Low dimensional materials (LDMs) have drawn world-wide attention as potential candidates applied in flexible and wearable electronics. It is an attractive research topic to systematically integrate all-LDMs to realize flexible electronics. However, it is difficult to pattern LDMs by conventional photolithography and plasma etching without harming the other overlapped analogous components. Here, we propose and realize independent-operation all-LDM flexible transistors integrated into a 2-inch substrate using the proposed photolithography incorporated filtration (PIF) platform. The transistors consisting of only one-dimensional carbon nanotubes and two-dimensional graphene oxide show an ultralow operating voltage of less than -1 V, an extraordinary subthreshold swing (SS) of 170 mV dec-1, a low threshold voltage (Vth) of -0.3 V and a high carrier mobility up to 105 cm2 V-1 s-1. Moreover, the device shows a small bending radius of 1 mm and a transistor transparency of 94%. The full room-temperature process further demonstrates the great potential of applying the proposed devices and the PIF platform to future high-performance flexible transparent electronics. This work provides a novel route to tackle the difficulty in integrating solution processed LDMs.

Precise Patterning of Organic Semiconductor Crystals for Integrated Device Applications

Development of high-performance organic electronic and optoelectronic devices relies on high-quality semiconducting crystals that have outstanding charge transport properties and long exciton diffusion length and lifetime. To achieve integrated device applications, it is a prerequisite to precisely locate the organic semiconductor crystals (OSCCs) to form a specifically patterned structure. Well-patterned OSCCs can not only reduce leakage current and cross-talk between neighboring devices, but also facilely integrate with other device elements and their corresponding interconnects. In this Review, general strategies for the patterning of OSCCs are summarized, and the advantages and limitations of different patterning methods are discussed. Discussion is focused on an advanced strategy for the high-resolution and wafer-scale patterning of OSCC by a surface microstructure-assisted patterning method. Furthermore, the recent progress on OSCC pattern-based integrated circuities is highlighted. Finally, the research challenges and directions of this young field are also presented.

Organic crystalline materials in flexible electronics

Flexible electronics have attracted considerable attention recently given their potential to revolutionize human lives. High-performance organic crystalline materials (OCMs) are considered strong candidates for next-generation flexible electronics such as displays, image sensors, and artificial skin. They not only have great advantages in terms of flexibility, molecular diversity, low-cost, solution processability, and inherent compatibility with flexible substrates, but also show less grain boundaries with minimal defects, ensuring excellent and uniform electronic characteristics. Meanwhile, OCMs also serve as a powerful tool to probe the intrinsic electronic and mechanical properties of organics and reveal the flexible device physics for further guidance for flexible materials and device design. While the past decades have witnessed huge advances in OCM-based flexible electronics, this review is intended to provide a timely overview of this fascinating field. First, the crystal packing, charge transport, and assembly protocols of OCMs are introduced. State-of-the-art construction strategies for aligned/patterned OCM on/into flexible substrates are then discussed in detail. Following this, advanced OCM-based flexible devices and their potential applications are highlighted. Finally, future directions and opportunities for this field are proposed, in the hope of providing guidance for future research.

Printed Thin-Film Transistors: Research from China

Thin-film transistors (TFTs) have experienced tremendous development during the past decades and show great promising applications in flat displays, sensors, radio frequency identification tags, logic circuit, and so on. The printed TFTs are the key components for rapid development and commercialization of printed electronics. The researchers in China play important roles to accelerate the development and commercialization of printed TFTs. In this review, we comprehensively summarize the research progress of printed TFTs on rigid and flexible substrates from China. The review will focus on printing techniques of TFTs, printed TFT components including semiconductors, dielectrics and electrodes, as well as fully printed TFTs and printed flexible TFTs. Furthermore, perspectives on the remaining challenges and future developments are proposed.

Multi-Valued Logic Circuits Based on Organic Anti-ambipolar Transistors

Multivalued logic circuits, which can handle more information than conventional binary logic circuits, have attracted much attention as a promising way to improve the data-processing capabilities of integrated circuits. In this study, we developed a ternary inverter based on organic field-effect transistors (OFET) as a potential component of high-performance and flexible integrated circuits. Key elements are anti-ambipolar and n-type OFETs connected in series. First, we demonstrate an organic ternary inverter that exhibits three distinct logic states. Second, the operating voltage was greatly reduced by taking advantage of an Al₂O₃ gate dielectric. Finally, the operating voltage was finely tuned by the designing of the device geometry. These results are achievable owing to the flexible controllability of the device configuration, suggesting that the organic ternary inverter plays an important role with regard to high-performance organic integrated circuits.

Nanofabrication of Conductive Metallic Structures on Elastomeric Materials

Existing techniques for patterning metallic structures on elastomers are limited in terms of resolution, yield and scalability. The primary constraint is the incompatibility of their physical properties with conventional cleanroom techniques. We demonstrate a reliable fabrication strategy to transfer high resolution metallic structures of <500 nm in dimension on elastomers. The proposed method consists of producing a metallic pattern using conventional lithographic techniques on silicon coated with a thin sacrificial aluminium layer. Subsequent wet etching of the sacrificial layer releases the elastomer with the embedded metallic pattern. Using this method, a nano-resistor with minimum feature size of 400 nm is fabricated on polydimethylsiloxane (PDMS) and applied in gas sensing. Adsorption of solvents in the PDMS causes swelling and increases the device resistance, which therefore enables the detection of volatile organic compounds (VOCs). Sensitivity to chloroform and toluene vapor with a rapid response (~30 s) and recovery (~200 s) is demonstrated using this PDMS nano-resistor at room temperature.

Covalent bonding-assisted nanotransfer lithography for the fabrication of plasmonic nano-optical elements

Many high-resolution patterning techniques have been developed to realize nano- and microscale applications of electric devices, sensors, and transistors. However, conventional patterning methods based on photo or e-beam lithography are not employed to fabricate optical elements of high aspect ratio and a sub-100 nm scale due to the limit of resolution, high costs and low throughput. In this study, covalent bonding-assisted nanotransfer lithography (CBNL) was proposed to fabricate various structures of high resolution and high aspect ratio at low cost by a robust and fast chemical reaction. The proposed process is based on the formation of covalent bonds between silicon of adhesive layers on a substrate and oxygen of the deposited material on the polymer stamp. The covalent bond is strong enough to detach multiple layers from the stamp for a large area without defects. The obtained nanostructures can be used for direct application or as a hard mask for etching. Two nano-optical applications were demonstrated in this study, i.e., a meta-surface and a wire-grid polarizer. A perfect absorption meta-surface was generated by transferring subwavelength hole arrays onto a substrate without any post-processing procedures. In addition, a wire-grid polarizer with high aspect ratio (1 : 3) and 50 nm line width was prepared by the nano-transfer of materials, which were used as a hard mask for etching. Therefore, CBNL provides a means of achieving large-area nano-optical elements with a simple roll-to-plate process at low cost.

Bio-compatible organic humidity sensor transferred to arbitrary surfaces fabricated using single-cell-thick onion membrane as both the substrate and sensing layer

A bio-compatible disposable organic humidity sensor has been fabricated that can be transferred to any arbitrary target surface. Single cell thick onion membrane has been used as the substrate while it also doubles as the active layer of the sensor. Two different types of sensors were fabricated. In type-1, the membrane was fixed into a plastic frame with IDT patterns on one side while the other side was also exposed to environment. In type-2, onion membrane was attached to a glass substrate with one side exposed to environment having an IDT screen-printed on top of it. The electrical output response of the sensors showed their ability to detect relative humidity between 0% RH and 80% RH with stable response and good sensitivity. The impedance of the sensors changed from 16 MΩ to 2 MΩ for type-1 and 6 MΩ to 20 KΩ for type-2. The response times of type-1 and type-2 were ~1 and 1.5 seconds respectively. The recovery times were ~10.75 seconds and ~11.25 seconds for type-1 and type-2 respectively. The device was successfully transferred to various randomly shaped surfaces without damaging the device.

Charge Transport in Organic and Polymeric Semiconductors for Flexible and Stretchable Devices

An ultimate goal of organic electronics is to fabricate large-area electronic devices and circuits on flexible and stretchable substrates. To achieve this target, understanding and/or tuning of the processes that determine charge transport is therefore of paramount importance for the development of high-performance devices, e.g., organic field-effect transistors (OFETs). Significant progress in this field is summarized here, with particular focus on the new insights of charge transport under certain strain effects in flexible and stretchable OFETs.

A Bioactive Carbon Nanotube-Based Ink for Printing 2D and 3D Flexible Electronics

The development of electrically conductive carbon nanotube-based inks is reported. Using these inks, 2D and 3D structures are printed on various flexible substrates such as paper, hydrogels, and elastomers. The printed patterns have mechanical and electrical properties that make them beneficial for various biological applications.

Alignment and Patterning of Ordered Small-Molecule Organic Semiconductor Micro-/Nanocrystals for Device Applications

Large-area alignment and patterning of small-molecule organic semiconductor micro-/nanocrystals (SMOSNs) at desired locations is a prerequisite for their practical device applications. Recent strategies for alignment and patterning of ordered SMOSNs and their corresponding device applications are highlighted.