Showing papers on "Flexible electronics published in 2021"

Cellulose-Based Flexible Functional Materials for Emerging Intelligent Electronics.

Abstract: There is currently enormous and growing demand for flexible electronics for personalized mobile equipment, human-machine interface units, wearable medical-healthcare systems, and bionic intelligent robots. Cellulose is a well-known natural biopolymer that has multiple advantages including low cost, renewability, easy processability, and biodegradability, as well as appealing mechanical performance, dielectricity, piezoelectricity, and convertibility. Because of its multiple merits, cellulose is frequently used as a substrate, binder, dielectric layer, gel electrolyte, and derived carbon material for flexible electronic devices. Leveraging the advantages of cellulose to design advanced functional materials will have a significant impact on portable intelligent electronics. Herein, the unique molecular structure and nanostructures (nanocrystals, nanofibers, nanosheets, etc.) of cellulose are briefly introduced, the structure-property-application relationships of cellulosic materials summarized, and the processing technologies for fabricating cellulose-based flexible electronics considered. The focus then turns to the recent advances of cellulose-based functional materials toward emerging intelligent electronic devices including flexible sensors, optoelectronic devices, field-effect transistors, nanogenerators, electrochemical energy storage devices, biomimetic electronic skins, and biological detection devices. Finally, an outlook of the potential challenges and future prospects for developing cellulose-based wearable devices and bioelectronic systems is presented.

Advanced Nanocellulose-Based Composites for Flexible Functional Energy Storage Devices.

Abstract: With the increasing demand for wearable electronics (such as smartwatch equipment, wearable health monitoring systems, and human-robot interface units), flexible energy storage systems with eco-friendly, low-cost, multifunctional characteristics, and high electrochemical performances are imperative to be constructed. Nanocellulose with sustainable natural abundance, superb properties, and unique structures has emerged as a promising nanomaterial, which shows significant potential for fabricating functional energy storage systems. This review is intended to provide novel perspectives on the combination of nanocellulose with other electrochemical materials to design and fabricate nanocellulose-based flexible composites for advanced energy storage devices. First, the unique structural characteristics and properties of nanocellulose are briefly introduced. Second, the structure-property-application relationships of these composites are addressed to optimize their performances from the perspective of processing technologies and micro/nano-interface structure. Next, the recent specific applications of nanocellulose-based composites, ranging from flexible lithium-ion batteries and electrochemical supercapacitors to emerging electrochemical energy storage devices, such as lithium-sulfur batteries, sodium-ion batteries, and zinc-ion batteries, are comprehensively discussed. Finally, the current challenges and future developments in nanocellulose-based composites for the next generation of flexible energy storage systems are proposed.

Electrospinning of Flexible Poly(vinyl alcohol)/MXene Nanofiber-Based Humidity Sensor Self-Powered by Monolayer Molybdenum Diselenide Piezoelectric Nanogenerator

Abstract: Two-dimensional material has been widely investigated for potential applications in sensor and flexible electronics. In this work, a self-powered flexible humidity sensing device based on poly(vinyl alcohol)/Ti3C2Tx (PVA/MXene) nanofibers film and monolayer molybdenum diselenide (MoSe2) piezoelectric nanogenerator (PENG) was reported for the first time. The monolayer MoSe2-based PENG was fabricated by atmospheric pressure chemical vapor deposition techniques, which can generate a peak output of 35 mV and a power density of 42 mW m−2. The flexible PENG integrated on polyethylene terephthalate (PET) substrate can harvest energy generated by different parts of human body and exhibit great application prospects in wearable devices. The electrospinned PVA/MXene nanofiber-based humidity sensor with flexible PET substrate under the driven of monolayer MoSe2 PENG, shows high response of ∼40, fast response/recovery time of 0.9/6.3 s, low hysteresis of 1.8% and excellent repeatability. The self-powered flexible humidity sensor yields the capability of detecting human skin moisture and ambient humidity. This work provides a pathway to explore the high-performance humidity sensor integrated with PENG for the self-powered flexible electronic devices.

3D Printed Flexible Strain Sensors: From Printing to Devices and Signals

Abstract: The revolutionary and pioneering advancements of flexible electronics provide the boundless potential to become one of the leading trends in the exploitation of wearable devices and electronic skin. Working as substantial intermediates for the collection of external mechanical signals, flexible strain sensors that get intensive attention are regarded as indispensable components in flexible integrated electronic systems. Compared with conventional preparation methods including complicated lithography and transfer printing, 3D printing technology is utilized to manufacture various flexible strain sensors owing to the low processing cost, superior fabrication accuracy, and satisfactory production efficiency. Herein, up-to-date flexible strain sensors fabricated via 3D printing are highlighted, focusing on different printing methods based on photocuring and materials extrusion, including Digital Light Processing (DLP), fused deposition modeling (FDM), and direct ink writing (DIW). Sensing mechanisms of 3D printed strain sensors are also discussed. Furthermore, the existing bottlenecks and future prospects are provided for further progressing research.

Wide Bandgap Oxide Semiconductors: from Materials Physics to Optoelectronic Devices

Abstract: Wide bandgap oxide semiconductors constitute a unique class of materials that combine properties of electrical conductivity and optical transparency. They are being widely used as key materials in optoelectronic device applications, including flat-panel displays, solar cells, OLED, and emerging flexible and transparent electronics. In this article, an up-to-date review on both the fundamental understanding of materials physics of oxide semiconductors, and recent research progress on design of new materials and high-performing thin film transistor (TFT) devices in the context of fundamental understanding is presented. In particular, an in depth overview is first provided on current understanding of the electronic structures, defect and doping chemistry, optical and transport properties of oxide semiconductors, which provide essential guiding principles for new material design and device optimization. With these principles, recent advances in design of p-type oxide semiconductors, new approaches for achieving cost-effective transparent (flexible) electrodes, and the creation of high mobility 2D electron gas (2DEG) at oxide surfaces and interfaces with a wealth of fascinating physical properties of great potential for novel device design are then reviewed. Finally, recent progress and perspective of oxide TFT based on new oxide semiconductors, 2DEG, and low-temperature solution processed oxide semiconductor for flexible electronics will be reviewed.

Electrospun nanofiber-based soft electronics

Abstract: Electrospun nanofibers have received considerable attention in the field of soft electronics owing to their promising advantages and superior properties in flexibility and/or stretchability, conductivity, and transparency; furthermore, their one-dimensional nanostructure, high surface area, and diverse fibrous morphologies are also desirable. Herein, we provide an overview of electrospun nanofiber-based soft electronics. A brief introduction of the unique structure and properties of electrospun nanofiber materials is provided, and assembly strategies for flexible/stretchable electronics are highlighted. We then summarize the latest progress in the design and fabrication of representative flexible/stretchable electronic devices utilizing electrospun nanofibers, such as flexible/stretchable conductors, sensors, energy harvesting and storage devices, and transistors. Finally, a conclusion and several future research directions for electrospun nanofiber-based soft electronics are proposed. The development of low-cost, efficient, and large-scale methods for fabricating ‘soft’ electronics, conducting materials with improved flexibility and stretchability, increases the range of possible applications. Flexible electronics are useful for foldable displays, healthcare monitoring, artificial skins and implantable bioelectronics. One approach to fabricating these devices is to construct them from conductive nanofibers. Takao Someya from the University of Tokyo and colleagues review recent advances in constructing nanofiber-based soft electronics using a technique called electrospinning. Electrospinning works by drawing a molten material through a nozzle into an electric field to produce strands much finer than a human hair. The authors review the structure and properties of electrospun nanofiber materials and the various strategies for assembling flexible and stretchable electronic devices such as sensors, transistors, and components for energy harvesting and storage. This review introduce the structure and properties of electrospun nanofiber materials and the various strategies for assembling soft electronic devices such as sensors, transistors, and components for energy harvesting and storage.

Recent progress in silk fibroin-based flexible electronics.

Abstract: With the rapid development of the Internet of Things (IoT) and the emergence of 5G, traditional silicon-based electronics no longer fully meet market demands such as nonplanar application scenarios due to mechanical mismatch. This provides unprecedented opportunities for flexible electronics that bypass the physical rigidity through the introduction of flexible materials. In recent decades, biological materials with outstanding biocompatibility and biodegradability, which are considered some of the most promising candidates for next-generation flexible electronics, have received increasing attention, e.g., silk fibroin, cellulose, pectin, chitosan, and melanin. Among them, silk fibroin presents greater superiorities in biocompatibility and biodegradability, and moreover, it also possesses a variety of attractive properties, such as adjustable water solubility, remarkable optical transmittance, high mechanical robustness, light weight, and ease of processing, which are partially or even completely lacking in other biological materials. Therefore, silk fibroin has been widely used as fundamental components for the construction of biocompatible flexible electronics, particularly for wearable and implantable devices. Furthermore, in recent years, more attention has been paid to the investigation of the functional characteristics of silk fibroin, such as the dielectric properties, piezoelectric properties, strong ability to lose electrons, and sensitivity to environmental variables. Here, this paper not only reviews the preparation technologies for various forms of silk fibroin and the recent progress in the use of silk fibroin as a fundamental material but also focuses on the recent advanced works in which silk fibroin serves as functional components. Additionally, the challenges and future development of silk fibroin-based flexible electronics are summarized.

A natively flexible 32-bit Arm microprocessor.

Abstract: Nearly 50 years ago, Intel created the world’s first commercially produced microprocessor—the 4004 (ref. 1), a modest 4-bit CPU (central processing unit) with 2,300 transistors fabricated using 10 μm process technology in silicon and capable only of simple arithmetic calculations. Since this ground-breaking achievement, there has been continuous technological development with increasing sophistication to the stage where state-of-the-art silicon 64-bit microprocessors now have 30 billion transistors (for example, the AWS Graviton2 (ref. 2) microprocessor, fabricated using 7 nm process technology). The microprocessor is now so embedded within our culture that it has become a meta-invention—that is, it is a tool that allows other inventions to be realized, most recently enabling the big data analysis needed for a COVID-19 vaccine to be developed in record time. Here we report a 32-bit Arm (a reduced instruction set computing (RISC) architecture) microprocessor developed with metal-oxide thin-film transistor technology on a flexible substrate (which we call the PlasticARM). Separate from the mainstream semiconductor industry, flexible electronics operate within a domain that seamlessly integrates with everyday objects through a combination of ultrathin form factor, conformability, extreme low cost and potential for mass-scale production. PlasticARM pioneers the embedding of billions of low-cost, ultrathin microprocessors into everyday objects. Flexible electronic platforms would enable the integration of functional electronic circuitry with many everyday objects; here, a low-cost and fully flexible 32-bit microprocessor is produced.

Recent advances of hydrogel electrolytes in flexible energy storage devices

Abstract: Novel flexible storage devices such as supercapacitors and rechargeable batteries are of great interest due to their broad potential applications in flexible electronics and implants. Hydrogels are crosslinked hydrophilic polymer networks filled with water, and considered one of the most promising electrolyte candidates due to their high-water absorbency and softness that fulfilled the fundamental requirements for flexible energy storage devices. Moreover, diverse properties such as self-healing ability, ultra-stretchability, electrochromism, and extreme-temperature resistance can be achieved by modifying the chemical structures, opening the door to the development of novel flexible energy storage devices with prolonged service life and scintillating functions. In this review, we discuss the design methods of recent hydrogel electrolytes for supercapacitors and batteries regarding their electrochemical performance and highlight those with exceptional breakthrough and additional functions. Finally, challenges and prospects of future development are explored.

Recent Progress of Flexible Image Sensors for Biomedical Applications.

Abstract: Flexible image sensors have attracted increasing attention as new imaging devices owing to their lightness, softness, and bendability. Since light can measure inside information from outside of the body, optical-imaging-based approaches, such as X-rays, are widely used for disease diagnosis in hospitals. Unlike conventional sensors, flexible image sensors are soft and can be directly attached to a curved surface, such as the skin, for continuous measurement of biometric information with high accuracy. Therefore, they are expected to gain wide application to wearable devices, as well as home medical care. Herein, the application of such sensors to the biomedical field is introduced. First, their individual components, photosensors, and switching elements, are explained. Then, the basic parameters used to evaluate the performance of each of these elements and the image sensors are described. Finally, examples of measuring the dynamic and static biometric information using flexible image sensors, together with relevant real-world measurement cases, are presented. Furthermore, recent applications of the flexible image sensors in the biomedical field are introduced.

High-performance flexible nanoscale transistors based on transition metal dichalcogenides

Abstract: Two-dimensional (2D) semiconducting transition metal dichalcogenides could be used to build high-performance flexible electronics. However, flexible field-effect transistors (FETs) based on such materials are typically fabricated with channel lengths on the micrometre scale, not benefitting from the short-channel advantages of 2D materials. Here, we report flexible nanoscale FETs based on 2D semiconductors; these are fabricated by transferring chemical-vapour-deposited transition metal dichalcogenides from rigid growth substrates together with nano-patterned metal contacts, using a polyimide film, which becomes the flexible substrate after release. Transistors based on monolayer molybdenum disulfide (MoS2) are created with channel lengths down to 60 nm and on-state currents up to 470 μA μm−1 at a drain–source voltage of 1 V, which is comparable to the performance of flexible graphene and crystalline silicon FETs. Despite the low thermal conductivity of the flexible substrate, we find that heat spreading through the metal gate and contacts is essential to reach such high current densities. We also show that the approach can be used to create flexible FETs based on molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). By transferring two-dimensional semiconductors from rigid growth substrates together with nano-patterned metal contacts, flexible field-effect transistors can be fabricated with channel lengths down to 60 nm.

Recent Trends and Developments in Conducting Polymer Nanocomposites for Multifunctional Applications.

Abstract: Electrically-conducting polymers (CPs) were first developed as a revolutionary class of organic compounds that possess optical and electrical properties comparable to that of metals as well as inorganic semiconductors and display the commendable properties correlated with traditional polymers, like the ease of manufacture along with resilience in processing. Polymer nanocomposites are designed and manufactured to ensure excellent promising properties for anti-static (electrically conducting), anti-corrosion, actuators, sensors, shape memory alloys, biomedical, flexible electronics, solar cells, fuel cells, supercapacitors, LEDs, and adhesive applications with desired-appealing and cost-effective, functional surface coatings. The distinctive properties of nanocomposite materials involve significantly improved mechanical characteristics, barrier-properties, weight-reduction, and increased, long-lasting performance in terms of heat, wear, and scratch-resistant. Constraint in availability of power due to continuous depletion in the reservoirs of fossil fuels has affected the performance and functioning of electronic and energy storage appliances. For such reasons, efforts to modify the performance of such appliances are under way through blending design engineering with organic electronics. Unlike conventional inorganic semiconductors, organic electronic materials are developed from conducting polymers (CPs), dyes and charge transfer complexes. However, the conductive polymers are perhaps more bio-compatible rather than conventional metals or semi-conductive materials. Such characteristics make it more fascinating for bio-engineering investigators to conduct research on polymers possessing antistatic properties for various applications. An extensive overview of different techniques of synthesis and the applications of polymer bio-nanocomposites in various fields of sensors, actuators, shape memory polymers, flexible electronics, optical limiting, electrical properties (batteries, solar cells, fuel cells, supercapacitors, LEDs), corrosion-protection and biomedical application are well-summarized from the findings all across the world in more than 150 references, exclusively from the past four years. This paper also presents recent advancements in composites of rare-earth oxides based on conducting polymer composites. Across a variety of biological and medical applications, the fact that numerous tissues were receptive to electric fields and stimuli made CPs more enticing.

Recent progress for silver nanowires conducting film for flexible electronics

Abstract: Silver nanowires (AgNWs), as one-dimensional nanometallic materials, have attracted wide attention due to the excellent electrical conductivity, transparency and flexibility, especially in flexible and stretchable electronics. However, the microscopic discontinuities require AgNWs be attached to some carrier for practical applications. Relative to the preparation method, how to integrate AgNWs into the flexible matrix is particularly important. In recent years, plenty of papers have been published on the preparation of conductors based on AgNWs, including printing techniques, coating techniques, vacuum filtration techniques, template-assisted assembly techniques, electrospinning techniques and gelating techniques. The aim of this review is to discuss different assembly method of AgNW-based conducting film and their advantages. Conducting films based on silver nanowires (AgNWs) have been reviewed with a focus on their assembly and their advantages.

Flexible and thin multifunctional waterborne polyurethane/Ag film for high-efficiency electromagnetic interference shielding, electro-thermal and strain sensing performances

Abstract: With the rapid development of the flexible electronics industry, the range of multifunctional applications of materials has become extensive But it is still a challenge to apply flexible materials to different fields while ensuring corresponding performance Herein, a simple and available approach is addressed to fabricate conductive polymer composite films supported on Ag flakes and waterborne polyurethane (WPU) by spraying The WPU/Ag films with uniform structure show outstanding flexibility and electromagnetic interference shielding effectiveness of 689 dB with thickness of only 50 μm, and could sustain a high standard even undergoing excessive mechanical deformations Besides, the resulted films possess prominent electro-thermal effect, which can achieve a temperature of over 120 °C by applying a low voltage of 2 V, and the heat can be dissipated rapidly along with the connecting Ag network Moreover, it shows a high gauge factor (2292), good durability and reproductivity (over 1000 cycles), and rapid response time to strain (50 ms), which can be potentially used in the field of human movement monitoring and wearable electronic devices These results indicate the multifunction of the WPU/Ag film, which could widen its practical applications after the corresponding treatment

Salt-mediated triple shape-memory ionic conductive polyampholyte hydrogel for wearable flexible electronics

Abstract: Wearable flexible electronics (WFEs) made of multifunctional hydrogels provide an approach for monitoring the human health such as human activities and human sweat. However, it is still necessary to develop a stimulus-responsive hydrogel sensor with the shape-memory effect (SME) to broaden the applications. Herein, we designed and fabricated a type of supramolecular polyampholyte hydrogel with salt-mediated triple SME, ionic conductivity (0.24–3.06 S m−1), high stretchability (up to 1500%) and self-healing property (up to 70%), which can be applied as shape-memory sensor and strain sensor. The SME endowed the sensors with the ability to detect the concentration changes in a saline solution by visual shape transformation. The conductivity caused the sensors to react with an instant electric signal when they detected human motion, while the stretchability allowed the sensors to bear large-scale mechanical deformation. The spontaneous self-healing and self-adhesive capabilities gave the sensors higher reliability, extended lifetime, and good attachment to human skin. Therefore, this multifunctional hydrogel can be a good candidate for precisely and conveniently monitoring the human health.

Self-healable and recyclable polyurethane-polyaniline hydrogel toward flexible strain sensor

Abstract: Flexible electronics have been extensively investigated in recent years because of their potential applications in artificial skin, soft robotics, energy storage, healthcare technology, etc. However, since the rigid and brittle nature of the conductive or semi-conductive materials, it's a huge challenge to project stretchable, self-healable and recyclable soft electronics to mimic skin. Herein, the interpenetrating and synergistic dual-network hydrogel of Diels-Alder chemistry-based dynamic polyurethane substrates and polyaniline conductive polymer (PU-DA-1/1-PANI) was prepared and employed as a strain sensor. The PU-DA-1/1-PANI hydrogel exhibited large elongation at break of 500%, soft Young's modulus of 0.3 MPa, and robust tensile strength of 1.1 MPa. Meanwhile, the strain sensors with optimized composition presented an ideal conductivity of 7.9 S m−1, which could monitor the physical motions precisely and repeatedly with a gauge factor (GF) of 2.9. In addition, the mechanical performance and conductivity could be self-healed, which was enabled by the hydrogen bonds, ionic interactions, reversible DA covalent bonds, and rearrangement of polymer chains. Built on the thermally stimuli-responsive nature of the DA covalent cross-linking points, the PU-DA-1/1-PANI composites could be recycled.

3D-Printed highly stretchable conducting polymer electrodes for flexible supercapacitors

Abstract: Recent advances in the development of wearable, implantable, and bio-integrated electronic devices have increased the demand for stretchable and flexible energy storage devices that can deliver high degrees of mechanical deformability. However, the fabrication of fully flexible electronics with both satisfactory electrochemical performance and mechanical stretchability remains a significant technological hurdle. In this work, by synergistically combining theoretical structural design and 3D printing, additive-free free-standing stretchable electrodes with different negative Poisson's ratio (NPR) structures have been developed based on a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) ink. Through tensile tests and finite element analyses (FEA), the stretchable electrode with a well-designed arc-shaped NPR structure can effectively reduce the peak strain, resulting in excellent flexibility (up to 180°) and stretchability (maximum elongation 150%). Through further integration of carbon nanotubes (CNTs), the 3D printed hybrid polymer/CNT electrode exhibits enhanced electrochemical performance with a high area capacitance of 990 mF cm−2. The as-fabricated quasi-solid-state symmetric supercapacitor not only achieves a satisfactory energy density and maintains excellent capacitance retention of 74.7% after 14 000 cycles, but also shows promising mechanical properties by maintaining stable power output even when being extremely deformed. The strategy proposed here offers promising opportunities in developing novel deformable electrodes for integrated wearable energy storage devices in various applications.

Imperceptible energy harvesting device and biomedical sensor based on ultraflexible ferroelectric transducers and organic diodes.

Abstract: Energy autonomy and conformability are essential elements in the next generation of wearable and flexible electronics for healthcare, robotics and cyber-physical systems. This study presents ferroelectric polymer transducers and organic diodes for imperceptible sensing and energy harvesting systems, which are integrated on ultrathin (1-µm) substrates, thus imparting them with excellent flexibility. Simulations show that the sensitivity of ultraflexible ferroelectric polymer transducers is strongly enhanced by using an ultrathin substrate, which allows the mounting on 3D-shaped objects and the stacking in multiple layers. Indeed, ultraflexible ferroelectric polymer transducers have improved sensitivity to strain and pressure, fast response and excellent mechanical stability, thus forming imperceptible wireless e-health patches for precise pulse and blood pressure monitoring. For harvesting biomechanical energy, the transducers are combined with rectifiers based on ultraflexible organic diodes thus comprising an imperceptible, 2.5-µm thin, energy harvesting device with an excellent peak power density of 3 mW·cm−3. Next-generation energy autonomous biomedical devices must easily conform to human skin, provide accurate health monitoring and allow for scalable manufacturing. Here, the authors report ultraflexible ferroelectric transducers and organic diodes for biomedical sensing and energy harvesting. Ultraflexible ferroelectric transducers based on P(VDF:TrFE) co-polymer with optimised crystalline structure by thermal annealing are utilised as sensors for vital parameters detection and as piezoelectric nanogenerators (PENG). The PENGs were incorporated in an energy harvesting system including OTFT-based rectifying circuits and thin film capacitors on a single ultrathin substrate. Both developments could pave the way towards self-powering, imperceptible e-health systems.

Material innovation and mechanics design for substrates and encapsulation of flexible electronics: a review

Abstract: Advances in materials and mechanics designs have led to the development of flexible electronics, which have important applications to human healthcare due to their good biocompatibility and conformal integration with biological tissue. Material innovation and mechanics design have played a key role in designing the substrates and encapsulations of flexible electronics for various bio-integrated systems. This review first introduces the inorganic materials and novel organic materials used for the substrates and encapsulation of flexible electronics, and summarizes their mechanics properties, permeability and optical transmission properties. The structural designs of the substrates are then introduced to ensure the reliability of flexible electronics, including the patterned and pre-strained designs to improve the stretchability, and the strain-isolation and -limiting substrates to reduce the deformation. Some emerging encapsulations are presented to protect the flexible electronics from degradation, environmental erosion or contamination, though they may slightly reduce the stretchability of flexible electronics.

Stencil Printing of Liquid Metal upon Electrospun Nanofibers Enables High-Performance Flexible Electronics.

Abstract: Flexible electronics as an emerging technology has demonstrated potential for applications in various fields. With the advent of the Internet of Things era, countless flexible electronic systems need to be developed and deployed. However, materials and fabrication technologies are the key factors restricting the development and commercialization of flexible electronics. Here we report a simple, fast, and green flexible electronics preparation technology. The stencil printing method is adopted to pattern liquid metal on the thermoplastic polyurethane membrane prepared by electrospinning. Besides, with layer-by-layer assembly, flexible circuits, resistors, capacitors, inductors, and their composite devices can be prepared parametrically. Furthermore, these devices have good stretchability, air permeability, and stability, while they are multilayered and reconfigurable. As proof, this strategy is used to fabricate flexible displays, flexible sensors, and flexible filters. Finally, flexible electronic devices are also recycled and reconfigured.