Flexible, Print-in-Place 1D-2D Thin-Film Transistors Using Aerosol Jet Printing

In this work, we overcome temperature constraints and demonstrate 1D−2D thin-film transistors (1D−2D TFTs) in a low-temperature (maximum exposure ≤80 °C) full print-in-place process (i.e., no substrate removal from printer throughout the entire process) using an aerosol jet printer. Semiconducting 1D CNT channels are used with a 2D hexagonal boron nitride (h-BN) gate dielectric and traces of silver nanowires as the conductive electrodes, all deposited using the same printer. The aerosol jet-printed 2D h-BN films were realized via proper ink formulation, such as utilizing the binder hydroxypropyl methylcellulose, which suppresses redispersion between adjacent printed layers. In addition to an ON/ OFF current ratio up to 3.5 Å~ 105, channel mobility up to 10.7 cm2·V-1·s-1, and low gate hysteresis, 1D−2D TFTs exhibit extraordinary mechanical stability under bending due to the nanoscale network structure of each layer, with minimal changes in performance after 1000 bending test cycles at 2.1% strain. It is also confirmed that none of the device layers require high-temperature treatment to realize optimal performance. These findings provide an attractive approach toward a cost-effective, direct-write realization of electronics

The 2021 flexible and printed electronics roadmap

This roadmap includes the perspectives and visions of leading researchers in the key areas of flexible and printable electronics. The covered topics are broadly organized by the device technologies (sections 1–9), fabrication techniques (sections 10–12), and design and modeling approaches (sections 13 and 14) essential to the future development of new applications leveraging flexible electronics (FE). The interdisciplinary nature of this field involves everything from fundamental scientific discoveries to engineering challenges; from design and synthesis of new materials via novel device design to modelling and digital manufacturing of integrated systems. As such, this roadmap aims to serve as a resource on the current status and future challenges in the areas covered by the roadmap and to highlight the breadth and wide-ranging opportunities made available by FE technologies

Active Matrix Flexible Sensory Systems: Materials, Design, Fabrication, and Integration

A variety of modern applications including soft robotics, prosthetics, and health monitoring devices that cover electronic skins (e-skins), wearables as well as implants have been developed within the last two decades to bridge the gap between artificial and biological systems. During this development, high-density integration of various sensing modalities into flexible electronic devices becomes vitally important to improve the perception and interaction of the human bodies and robotic appliances with external environment. As a key component in flexible electronics, the flexible thin-film transistors (TFTs) have seen significant advances, allowing for building flexible active matrices. The flexible active matrices have been integrated with distributed arrays of sensing elements, enabling the detection of signals over a large area. The integration of sensors within pixels of flexible active matrices has brought the application scenarios to a higher level of sophistication with many advanced functionalities. Herein, recent progress in the active matrix flexible sensory systems is reviewed. The materials used to construct the semiconductor channels, the dielectric layers, and the flexible substrates for the active matrices are summarized. The pixel designs and fabrication strategies for the active matrix flexible sensory systems are briefly discussed. The applications of the flexible sensory systems are exemplified by reviewing pressure sensors, temperature sensors, photodetectors, magnetic sensors, and biosignal sensors. At the end, the recent development is summarized and the vision on the further advances of flexible active matrix sensory systems is provided

Hybrid Nanomaterials

Two of the hottest research topics today are hybrid nanomaterials and flexible electronics. As such, this book covers both topics with chapters written by experts from across the globe. Chapters address hybrid nanomaterials, electronic transport in black phosphorus, three-dimensional nanocarbon hybrids, hybrid ion exchangers, pressure-sensitive adhesives for flexible electronics, simulation and modeling of transistors, smart manufacturing technologies, and inorganic semiconductors

Flexible antenna arrays and transistor devices fabricated using inkjet printing techniques

This dissertation reports several improvements to the current state of the art in inkjet printed electronics, including new material formulations and new techniques which allow for smaller negative dimensions than had previously been reported. These new techniques and materials are used to produce several different types of devices on flexible substrates, including a new type of printed array antenna called the frequency scanning array as well as both high performance and high throughput producible transistors. The experiences of building these devices are then used to synthesize potential approaches to integrating the unique advantages of printed electronics into conventional IC manufacturing processes. This arc from material development, to device development, and finally process improvement represents a complete holistic approach to the production of flexible printed electronics devices.Electrical and Computer Engineerin

Flexible Electronics for Neurological Electronic Skin with Multiple Sensing Modalities

The evolution of electronic skin (E-skin) technology in the past decade has resulted in a great variety of flexible electronic devices that mimic the physical and chemical sensing properties of skin for applications in advanced robotics, prosthetics, and health monitoring technologies. The further advancement of E-skin technology demands closer imitation of skin receptors\u27 transduction mechanisms, simultaneous detection of multiple information from different sources, and the study of transmission, processing and memory of the signals among the neurons. Motivated by such demands, this thesis focuses on design, fabrication, characterization of novel flexible electronic devices and integration of individual devices to realize prototype biomimetic E-skin with neurological and multimodal sensing functions. More specifically, we have studied flexible carbon nanotube thin-film transistors (CNT-TFTs) as control and signal processing units of E-skin and flexible ferroelectret nanogenerator (FENG) and triboelectric nanogenerator (TENG) as skin mechanoreceptors. Multiple fabrication methods, such as low-cost printing and conventional cleanroom-based microfabrication have been implemented to fabricate flexible CNT-TFTs with different structures and functions, especially the synaptic functions. Based on the research on individual devices, we have demonstrated a prototype force-sensing flexible neurological E-skin and its sensory nerve and synapse, with FENG serving as the sensory mechanoreceptor that generates action potentials (pulsed voltages) to be processed and transmitted by the flexible synaptic CNT-TFT. It allows for instantaneous detection of force stimuli and offers biological synapse-like behavior to store the stimulus information and relay the stimulus signals to the next stage. The force-sensing neurological E-skin was further augmented with visual and auditory sensing modalities by introducing phototransistor-based optical sensor and FENG-based acoustic sensor. Successful transduction of visual, auditory and tactile stimuli and synaptic processing and memory of those signals have all been demonstrated. Thanks to the multimodal sensing capability of the neurological E-skin, psychological associative learning experiment-“Pavlov’s dog\u27s experiment”, was also successfully implemented electronically by synergizing actual visual and auditory signals in the synaptic transistor. Flexible electronics and prototype neurological E-skin system demonstrated in this thesis may offer an entry into novel multimodal, user-environment interactive soft E-skin system for soft robotic and diagnostic applications

Solution Processing of Long Carbon Nanotubes: from Fundamentals to Applications

Single-walled carbon nanotubes (SWCNTs) are one of the most intensively studied nanomaterials due to their extraordinary mechanical, electrical, and optical properties. Attaining aqueous solutions of individual SWCNTs is the critical first step for harnessing their outstanding properties and applying them in many applications and further processing, such as sorting, imaging, and sensing. However, the current ultrasonication-then-ultracentrifugation approach inevitably introduces defects to SWCNTs and cuts the nanotubes into smaller pieces, compromising the electrical and mechanical properties of this otherwise remarkable material. In this dissertation, we introduce an unexpectedly simple approach that completely eliminates the need for ultrasonication, and nondestructively disperses SWCNTs in aqueous solution, so that the synthetic lengths of SWCNTs can be preserved. The dispersion is achieved by using surfactants to wrap and stabilize the protonated SWCNTs by simple acid-base neutralization reactions. The result is that the protons on SWCNTs are replaced by surfactants, and thus, we name this method “superacid-surfactant exchange (S2E).” In chapters 2-4, we demonstrate the length of dissolved SWCNTs by S2E can be 4-10 times longer than the sonicated controls, thereby significantly improving the optical, electrical and electromechanical properties. We further find that by tuning the concentrations of SWCNTs in this S2E process, short nanotubes can be selectively extracted out, allowing separation of the long carbon nanotubes (>10 µm). In chapter 5, we show that long SWCNTs can behave like mechanical reinforcing structures that enhance the mechanical strength of graphene through π-π interactions without sacrificing much of the outstanding transparency of graphene. This fact has enabled the fabrication of the mechanically strong yet ultrathin graphene/SWCNTs hybrid structure (G+T) for operando probing of the electrical double layer at the electrode-electrolyte interface by X-ray photoelectron. Finally, as a ramification result from the S2E process, chapter 6 describes the scalable synthesis of organic-color-center tailored SWCNTs

New materials and advances in making electronic skin for interactive robots

Flexible electronics has huge potential to bring revolution in robotics and prosthetics as well as to bring about the next big evolution in electronics industry. In robotics and related applications, it is expected to revolutionise the way with which machines interact with humans, real-world objects and the environment. For example, the conformable electronic or tactile skin on robot’s body, enabled by advances in flexible electronics, will allow safe robotic interaction during physical contact of robot with various objects. Developing a conformable, bendable and stretchable electronic system requires distributing electronics over large non-planar surfaces and movable components. The current research focus in this direction is marked by the use of novel materials or by the smart engineering of the traditional materials to develop new sensors, electronics on substrates that can be wrapped around curved surfaces. Attempts are being made to achieve flexibility/stretchability in e-skin while retaining a reliable operation. This review provides insight into various materials that have been used in the development of flexible electronics primarily for e-skin applications