Wearable Intrinsically Soft, Stretchable, Flexible Devices for Memories and Computing

A Brief Review on Flexible Electronics for IoT: Solutions for Sustainability and New Perspectives for Designers

The Internet of Things (IoT) is gaining more and more popularity and it is establishing itself in all areas, from industry to everyday life. Given its pervasiveness and considering the problems that afflict today's world, that must be carefully monitored and addressed to guarantee a future for the new generations, the sustainability of technological solutions must be a focal point in the activities of researchers in the field. Many of these solutions are based on flexible, printed or wearable electronics. The choice of materials therefore becomes fundamental, just as it is crucial to provide the necessary power supply in a green way. In this paper we want to analyze the state of the art of flexible electronics for the IoT, paying particular attention to the issue of sustainability. Furthermore, considerations will be made on how the skills required for the designers of such flexible circuits, the features required to the new design tools and the characterization of electronic circuits are changing.

Resistive random access memory: introduction to device mechanism, materials and application to neuromorphic computing

The modern-day computing technologies are continuously undergoing a rapid changing landscape; thus, the demands of new memory types are growing that will be fast, energy efficient and durable. The limited scaling capabilities of the conventional memory technologies are pushing the limits of data-intense applications beyond the scope of silicon-based complementary metal oxide semiconductors (CMOS). Resistive random access memory (RRAM) is one of the most suitable emerging memory technologies candidates that have demonstrated potential to replace state-of-the-art integrated electronic devices for advanced computing and digital and analog circuit applications including neuromorphic networks. RRAM has grown in prominence in the recent years due to its simple structure, long retention, high operating speed, ultra-low-power operation capabilities, ability to scale to lower dimensions without affecting the device performance and the possibility of three-dimensional integration for high-density applications. Over the past few years, research has shown RRAM as one of the most suitable candidates for designing efficient, intelligent and secure computing system in the post-CMOS era. In this manuscript, the journey and the device engineering of RRAM with a special focus on the resistive switching mechanism are detailed. This review also focuses on the RRAM based on two-dimensional (2D) materials, as 2D materials offer unique electrical, chemical, mechanical and physical properties owing to their ultrathin, flexible and multilayer structure. Finally, the applications of RRAM in the field of neuromorphic computing are presented.

Neuromorphic Liquids, Colloids, and Gels: A Review

Advances in flexible electronic devices and robotic software require that sensors and controllers be virtually devoid of traditional electronic components, be deformable and stretch-resistant. Liquid electronic devices that mimic biological synapses would make an ideal core component for flexible liquid circuits. This is due to their unbeatable features such as flexibility, reconfiguration, fault tolerance. To mimic synaptic functions in fluids we need to imitate dynamics and complexity similar to those that occurring in living systems. Mimicking ionic movements are considered as the simplest platform for implementation of neuromorphic in material computing systems. We overview a series of experimental laboratory prototypes where neuromorphic systems are implemented in liquids, colloids and gels.

Reconfigurable neuromorphic memristor network for ultralow-power smart textile electronics

Neuromorphic computing memristors are attractive to construct low-power- consumption electronic textiles due to the intrinsic interwoven architecture and promising applications in wearable electronics. Developing reconfigurable fiber-based memristors is an efficient method to realize electronic textiles that capable of neuromorphic computing function. However, the previously reported artificial synapse and neuron need different materials and configurations, making it difficult to realize multiple functions in a single device. Herein, a textile memristor network of Ag/MoS₂/HfAlO_x/carbon nanotube with reconfigurable characteristics was reported, which can achieve both nonvolatile synaptic plasticity and volatile neuron functions. In addition, a single reconfigurable memristor can realize integrate-and-fire function, exhibiting significant advantages in reducing the complexity of neuron circuits. The firing energy consumption of fiber-based memristive neuron is 1.9 fJ/spike (femtojoule-level), which is at least three orders of magnitude lower than that of the reported biological and artificial neuron (picojoule-level). The ultralow energy consumption makes it possible to create an electronic neural network that reduces the energy consumption compared to human brain. By integrating the reconfigurable synapse, neuron and heating resistor, a smart textile system is successfully constructed for warm fabric application, providing a unique functional reconfiguration pathway toward the next-generation in-memory computing textile system.

Study the Electrical Properties of Surface Mount Device Integrated Silver Coated Vectran Yarn

Smart textiles have attracted huge attention due to their potential applications for ease of life. Recently, smart textiles have been produced by means of incorporation of electronic components onto/into conductive metallic yarns. The development, characterizations, and electro-mechanical testing of surface mounted electronic device (SMD) integrated E-yarns is still limited. There is a vulnerability to short circuits as non-filament conductive yarns have protruding fibers. It is important to determine the best construction method and study the factors that influence the textile properties of the base yarn. This paper investigated the effects of different external factors, namely, strain, solder pad size, temperature, abrasion, and washing on the electrical resistance of SMD integrated silver-coated Vectran (SCV) yarn. For this, a Vectran E-yarn was fabricated by integrating the SMD resistor into a SCV yarn by applying a vapor phase reflow soldering method. The results showed that the conductive gauge length, strain, overlap solder pad size, temperature, abrasion, and washing had a significant effect on the electrical resistance property of the SCV E-yarn. In addition, based on the experiment, the E-yarn made from SCV conductive thread and 68 Ω SMD resistor had the maximum electrical resistance and power of 72.16 Ω and 0.29 W per 0.31 m length. Therefore, the structure of this E-yarn is also expected to bring great benefits to manufacturing wearable conductive tracks and sensors.

An Ultrastretchable Electrical Switch Fiber with a Magnetic Liquid Metal Core for Remote Magnetic Actuation

In this work we describe a soft and ultrastretchable fiber with a magnetic liquid metal (MLM) core for electrical switches used in remote magnetic actuation. MLM was prepared by removing the oxide layer on the liquid metal and subsequent mixing with magnetic iron particles. We used SEBS (poly[styrene-b-(ethylene-co-butylene)-b-styrene]) and silicone to prepare stretchable elastic fibers. Once hollow elastic fibers form, MLM was injected into the core of the fiber at ambient pressure. The fibers are soft (Young's modulus of 1.6~4.4 MPa) and ultrastretchable (elongation at break of 600~5000%) while maintaining electrical conductivity and magnetic property due to the fluidic nature of the core. Magnetic strength of the fibers was characterized by measuring the maximum effective distance between the magnet and the fiber as a function of iron particle concentration in the MLM core and the polymeric shell. The MLM core facilitates the use of the fiber in electrical switches for remote magnetic actuation. This ultrastretchable and elastic fiber with MLM core can be used in soft robotics, and wearable and conformal electronics.

Preparation parameters of polyaniline/polyvinyl chloride flexible wires for electrical conductivity performance analysis based on orthogonal arrays

A flexible polyaniline/polyvinyl chloride (PVC) polymer conductive wire was prepared using flexible PVC polymer as the substrate by the swelling – in-situ polymerization method, the line-shaped dents were pressed on the substrate by the thermodynamic pre-deformation treatment technology. Based on the orthogonal test method, the effects of five main influencing factors – swelling time (A), swelling temperature (B), oxidation temperature (C), oxidation time (D), and oxidant concentration (E) – on the conductivity of the prepared polyaniline/PVC conductive wire was investigated. The results of the orthogonal array testing were subjected to range analysis and analysis of variance (ANOVA), and the influencing factors, in terms of significance, follow the order of swelling temperature, oxidation time, swelling time, oxidation temperature, and oxidant concentration, with the optimal factor-level combination being A₂B₂C₂D₂E₂, which led to a desirable conductivity up to 1.19 × 10⁻¹ S/cm. In addition, the influence of different conductive line size characteristics on the molecular structure, microstructure, and conductivity of polyaniline/PVC flexible conductive wire was further studied. On the microstructure, as the line width increases, the infrared absorption intensity ratio of the quinone ring and the benzene ring in the polyaniline/PVC conductive wires gradually approaches 1. The microstructure, as the line width of the polyaniline/PVC conductive wire increases, the formed polyaniline gradually changes from flakes and granules to fibrous strips and entangles with each other to form a spatial network structure. The conductivity of the wire increases with the increase of its width up to 1.48 × 10⁻¹ S/cm.

High-Performance Vertical Organic Phototransistors Enhanced by Ferroelectrics

Organic phototransistors with high sensitivity and responsivity to light irradiance have great potential applications in national defense, meteorology, industrial manufacturing, and medical security. However, undesired dark current and photoresponsivity limit their practical applications. Here, a novel vertical organic phototransistor combined with ferroelectric materials is developed. The device structure has nanometer channel length, which can effectively separate photogenerated carriers and reduce the probability of carrier recombination and defect scattering, thus improving the device performance of phototransistors. Moreover, by inserting the poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) ferroelectric layer, the Schottky barrier at the interface between the semiconductor and source can be adjusted by the polarization of the external electric field, which can effectively reduce the dark current of the phototransistor to further improve the device performance. Therefore, our phototransistors exhibit a high photoresponsivity of more than 5.7 × 10⁵A/W, an outstanding detectivity of 1.15 × 10¹⁸ Jones, and an excellent photosensitivity of 5 × 10⁷ under 760 nm light illumination, which are better than those of conventional lateral organic phototransistors. This work provides a new approach for the development of high-performance phototransistors, which opens a new pathway for organic phototransistors in practical application.

Big Data and Atrial Fibrillation: Current Understanding and New Opportunities

Atrial fibrillation (AF) is the most common arrhythmia with diverse etiology that remarkably relates to high morbidity and mortality. With the advancements in intensive clinical and basic research, the understanding of electrophysiological and pathophysiological mechanism, as well as treatment of AF have made huge progress. However, many unresolved issues remain, including the core mechanisms and key intervention targets. Big data approach has produced new insights into the improvement of the situation. A large amount of data have been accumulated in the field of AF research, thus using the big data to achieve prevention and precise treatment of AF may be the direction of future development. In this review, we will discuss the current understanding of big data and explore the potential applications of big data in AF research, including predictive models of disease processes, disease heterogeneity, drug safety and development, precision medicine, and the potential source for big data acquisition. Grapical abstract.

Reactive fungal wearable

Smart wearables sense and process information from the user's body and environment and report results of their analysis as electrical signals. Conventional electronic sensors and controllers are commonly, sometimes augmented by recent advances in soft electronics. Organic electronics and bioelectronics, especially with living substrates, offer a great opportunity to incorporate parallel sensing and information processing capabilities of natural systems into future and emerging wearables. Nowadays fungi are emerging as a promising candidate to produce sustainable textiles to be used as ecofriendly biowearables. To assess the sensing potential of fungal wearables we undertook laboratory experiments on electrical response of a hemp fabric colonised by oyster fungi Pleurotus ostreatus to mechanical stretching and stimulation with attractants and repellents. We have shown that it is possible to discern a nature of stimuli from the fungi electrical responses. The results paved a way towards future design of intelligent sensing patches to be used in reactive fungal wearables.

The application of wearable smart sensors for monitoring the vital signs of patients in epidemics: a systematic literature review

Wearable smart sensors are emerging technology for daily monitoring of vital signs with the reducing discomfort and interference with normal human activities. The main objective of this study was to review the applied wearable smart sensors for disease control and vital signs monitoring in epidemics outbreaks. A comprehensive search was conducted in Web of Science, Scopus, IEEE Library, PubMed and Google Scholar databases to identify relevant studies published until June 2, 2020. Main extracted specifications for each paper are publication details, type of sensor, disease, type of monitored vital sign, function and usage. Of 277 articles, 11 studies were eligible for criteria. 36% of papers were published in 2020. Articles were published in 10 different journals and only in the Journal of Medical Systems more than one article was published. Most sensors were used to monitor body temperature, heart rate and blood pressure. Wearable devices (like a helmet, watch, or cuff) and body area network sensors were popular types which can be used monitoring vital signs for epidemic trending. 65% of total papers (n = 6) were conducted by the USA, Malaysia and India. Applying appropriate technological solutions could improve control and management of epidemic disease as well as the application of sensors for continuous monitoring of vital signs. However, further studies are needed to investigate the real effects of these sensors and their effectiveness.

Accuracy of Mobile Applications versus Wearable Devices in Long-Term Step Measurements

Fitness sensors and health systems are paving the way toward improving the quality of medical care by exploiting the benefits of new technology. For example, the great amount of patient-generated health data available today gives new opportunities to measure life parameters in real time and create a revolution in communication for professionals and patients. In this work, we concentrated on the basic parameter typically measured by fitness applications and devices-the number of steps taken daily. In particular, the main goal of this study was to compare the accuracy and precision of smartphone applications versus those of wearable devices to give users an idea about what can be expected regarding the relative difference in measurements achieved using different system typologies. In particular, the data obtained showed a difference of approximately 30%, proving that smartphone applications provide inaccurate measurements in long-term analysis, while wearable devices are precise and accurate. Accordingly, we challenge the reliability of previous studies reporting data collected with phone-based applications, and besides discussing the current limitations, we support the use of wearable devices for mHealth.

Sustainable resistance switching performance from composite-type ReRAM device based on carbon Nanotube@Titania core-shell wires

A novel nanocomposite-based non-volatile resistance switching random access memory device introducing single-walled carbon nanotube (SWCNT)@TiO₂ core–shell wires was proposed for flexible electronics. The SWCNT was de-bundled by ultrasonication with sodium dodecylbenzene sulfonate (SDBS), and then the TiO₂ skin layer on the SWCNT surface was successfully introduced by adding benzyl alcohol as a weak surfactant. The nanocomposite resistance switching layer was composed of the SWCNT@TiO₂ core–shell wires and poly(vinyl alcohol) (PVA) matrix by a simple spin-coating method. The device exhibited reproducible resistance switching performance with a remarkably narrow distribution of operating parameters (V_SET and V_RESET were 2.63 ± 0.16 and 0.95 ± 0.11 V, respectively) with a large R_ON/R_OFF ratio of 10⁵ for 200 consecutive switching cycles. Furthermore, the excellent resistance switching behavior in our device was maintained against mechanical stress up to 10⁵ bending test. We believe that the nanocomposite memory device with SWCNT@TiO₂ core–shell wires would be a critical asset to realize practical application for a flexible non-volatile memory field.

Using Stretchable PPy@PVA Composites as a High-Sensitivity Strain Sensor To Monitor Minute Motion

With the rapid development of flexible and wearable electronic devices, research on high-sensitivity strain sensors has been attracting much attention. Here, glutaraldehyde is used as a cross-linking reagent to precross-link poly(vinyl alcohol); then FeCl₃·6H₂O is added into the precross-linked poly(vinyl alcohol) to obtain composite films of FeCl₃@PVA after gelatinization and freeze drying. Elastic conductive films of polypyrrole@poly(vinyl alcohol) (PPy@PVA) are prepared by immersing FeCl₃@PVA into a solution of pyrrole in acetonitrile and water to complete the polymerization in situ. The effects of the concentrations of glutaraldehyde and FeCl₃·6H₂O on the film's structure and properties have been studied in detail; the results show that the strain sensor prepared from the optimized film has excellent stretchability (strain up to 309.5%), mechanical property (tensile strength of 32.8 MPa), and relatively high sensitivity (gauge factor can reach 5.07 under 1.0% strain). It can be used to detect various tiny physiological signals, for example, detecting the number of pulse beats, bending of the knuckles at different frequencies, and recognizing the pronunciation of different words by vocal cord vibration. These good properties mean that this kind of PPy@PVA strain sensor has great application prospects in physiological monitoring.

Light-Sensitive Material Structure-Electrical Performance Relationship for Optical Memory Transistors Incorporating Photochromic Dihetarylethenes

Photoswitchable organic field-effect transistors (OFETs) with embedded photochromic materials are considered as a promising platform for development of organic optical memory devices. Unfortunately, the operational mechanism of these devices and guidelines for selection of light-sensitive materials are still poorly explored. In the present work, a series of photochromic dihetarylethenes with a cyclopentenone bridge moiety were investigated as a dielectric/semiconductor interlayer in the structure of photoswitchable OFETs. It was shown that the electrical performance and stability of the devices can be tuned by variation of the substituents in the structure of the photochromic material. In particular, it was found that dihetarylethenes with donor substituents demonstrated the best light-induced switching effects (wider memory windows and higher switching coefficients) in the devices. The operation mechanism of the light-triggered memory devices was proposed based on the differential in situ Fourier transform infrared (FTIR) spectroscopy data and regression analysis of the threshold voltage-programming time experimental dependencies. The established relationships will facilitate further rational design of new photochromic materials, thus paving a way to fast and durable organic optical memories and memory transistors (memristors).

Machine-Washable Conductive Silk Yarns with a Composite Coating of Ag Nanowires and PEDOT:PSS

Electrically conducting fibers and yarns are critical components of future wearable electronic textile (e-textile) devices such as sensors, antennae, information processors, and energy harvesters. To achieve reliable wearable devices, the development of robust yarns with a high conductivity and excellent washability is urgently needed. In the present study, highly conductive and machine-washable silk yarns were developed utilizing a Ag nanowire and PEDOT:PSS composite coating. Ag nanowires were coated on the silk yarn via a dip-coating process followed by coating with the conjugated polymer:polyelectrolyte complex PEDOT:PSS. The PEDOT:PSS covered the Ag nanowire layers while electrostatically binding to the silk, which significantly improved the robustness of the yarn as compared with the Ag nanowire-coated reference yarns. The fabricated conductive silk yarns had an excellent bulk conductivity of up to ∼320 S/cm, which is largely retained even after several cycles of machine washing. To demonstrate that these yarns can be incorporated into e-textiles, the conductive yarns were used to construct an all-textile out-of-plane thermoelectric device and a Joule heating element in a woven heating fabric.

Advances in Liquid Metal-Enabled Flexible and Wearable Sensors

Sensors are core elements to directly obtain information from surrounding objects for further detecting, judging and controlling purposes. With the rapid development of soft electronics, flexible sensors have made considerable progress, and can better fit the objects to detect and, thus respond to changes more sensitively. Recently, as a newly emerging electronic ink, liquid metal is being increasingly investigated to realize various electronic elements, especially soft ones. Compared to conventional soft sensors, the introduction of liquid metal shows rather unique advantages. Due to excellent flexibility and conductivity, liquid-metal soft sensors present high enhancement in sensitivity and precision, thus producing many profound applications. So far, a series of flexible and wearable sensors based on liquid metal have been designed and tested. Their applications have also witnessed a growing exploration in biomedical areas, including health-monitoring, electronic skin, wearable devices and intelligent robots etc. This article presents a systematic review of the typical progress of liquid metal-enabled soft sensors, including material innovations, fabrication strategies, fundamental principles, representative application examples, and so on. The perspectives of liquid-metal soft sensors is finally interpreted to conclude the future challenges and opportunities.

Smart Textile-Integrated Microelectronic Systems for Wearable Applications

The programmable nature of smart textiles makes them an indispensable part of an emerging new technology field. Smart textile-integrated microelectronic systems (STIMES), which combine microelectronics and technology such as artificial intelligence and augmented or virtual reality, have been intensively explored. A vast range of research activities have been reported. Many promising applications in healthcare, the internet of things (IoT), smart city management, robotics, etc., have been demonstrated around the world. A timely overview and comprehensive review of progress of this field in the last five years are provided. Several main aspects are covered: functional materials, major fabrication processes of smart textile components, functional devices, system architectures and heterogeneous integration, wearable applications in human and nonhuman-related areas, and the safety and security of STIMES. The major types of textile-integrated nonconventional functional devices are discussed in detail: sensors, actuators, displays, antennas, energy harvesters and their hybrids, batteries and supercapacitors, circuit boards, and memory devices.

Printed Strain Gauge on 3D and Low-Melting Point Plastic Surface by Aerosol Jet Printing and Photonic Curing

Printing sensors and electronics directly on the objects is very attractive for producing smart devices, but it is still a challenge. Indeed, in some applications, the substrate that supports the printed electronics could be non-planar or the thermal curing of the functional inks could damage temperature-sensitive substrates such as plastics, fabric or paper. In this paper, we propose a new method for manufacturing silver-based strain sensors with arbitrary and custom geometries directly on plastic objects with curvilinear surfaces: (1) the silver lines are deposited by aerosol jet printing, which can print on non-planar or 3D surfaces; (2) photonic sintering quickly cures the deposited layer, avoiding the overheating of the substrate. To validate the manufacturing process, we printed strain gauges with conventional geometry on polyvinyl chloride (PVC) conduits. The entire manufacturing process, included sensor wiring and optional encapsulation, is performed at room temperature, compatible with the plastic surface. At the end of the process, the measured thickness of the printed sensor was 8.72 μm on average, the volume resistivity was evaluated 40 μΩ∙cm, and the thermal coefficient resistance was measured 0.150 %/°C. The average resistance was (71 ± 7) Ω and the gauge factor was found to be 2.42 on average.

Nanowire Electronics: From Nanoscale to Macroscale

Semiconductor nanowires have attracted extensive interest as one of the best-defined classes of nanoscale building blocks for the bottom-up assembly of functional electronic and optoelectronic devices over the past two decades. The article provides a comprehensive review of the continuing efforts in exploring semiconductor nanowires for the assembly of functional nanoscale electronics and macroelectronics. Specifically, we start with a brief overview of the synthetic control of various semiconductor nanowires and nanowire heterostructures with precisely controlled physical dimension, chemical composition, heterostructure interface, and electronic properties to define the material foundation for nanowire electronics. We then summarize a series of assembly strategies developed for creating well-ordered nanowire arrays with controlled spatial position, orientation, and density, which are essential for constructing increasingly complex electronic devices and circuits from synthetic semiconductor nanowires. Next, we review the fundamental electronic properties and various single nanowire transistor concepts. Combining the designable electronic properties and controllable assembly approaches, we then discuss a series of nanoscale devices and integrated circuits assembled from nanowire building blocks, as well as a unique design of solution-processable nanowire thin-film transistors for high-performance large-area flexible electronics. Last, we conclude with a brief perspective on the standing challenges and future opportunities.

Low-Voltage Organic Transistor Memory Fiber with a Nanograined Organic Ferroelectric Film

Wearable technology offers new ways to be more proactive about our health and surroundings in real time. For next-generation wearable systems, robust storage and recording media are required to monitor and process the essential electrical signals generated under various unpredictable strain conditions. Here, we report the first fibriform organic transistor memory integrated on a thin and flexible metal wire. A capillary tube coating system allows the formation of a thin and nanograined organic ferroelectric film on the wire. The uniform morphology imparts excellent switching stability (∼100 cycles), quasi-permanent retention (over 5 × 10⁴ s), and low-voltage operation (below 5 V) to the fiber-shaped memory devices. When sewn in a stretchable textile fabric, the memory fiber achieves long retention time of more than 10⁴ s with negligible degradation of memory window even under a constant diagonal strain of 100% that exhibits reliable data storage under tough environments. These results illustrate the possibility of the practical, wearable fiber memory for recording electronic signals in smart garment applications.

A Rapid Thermal Nanoimprint Apparatus through Induction Heating of Nickel Mold

Thermal nanoimprint lithography is playing a vital role in fabricating micro/nanostructures on polymer materials by the advantages of low cost, high throughput, and high resolution. However, a typical thermal nanoimprint process usually takes tens of minutes due to the relatively low heating and cooling rate in the thermal imprint cycle. In this study, we developed an induction heating apparatus for the thermal imprint with a mold made of ferromagnetic material, nickel. By applying an external high-frequency alternating magnetic field, heat was generated by the eddy currents and magnetic hysteresis losses of the ferromagnetic nickel mold at high speed. Once the external alternating magnetic field was cut off, the system would cool down fast owe to the small thermal capacity of the nickel mold; thus, providing a high heating and cooling rate for the thermal nanoimprint process. In this paper, nanostructures were successfully replicated onto polymer sheets with the scale of 4-inch diameter within 5 min.

Low-Cost Rapid Fabrication of Conformal Liquid-Metal Patterns

Patterned conformal conductive structures are used to realize flexible electronics for applications such as electronic skin, communication devices, and sensors. Thus, there is a demand for low-cost rapid fabrication techniques for flexible and stretchable conductors. Spray-coating of liquid metals is a prototyping method that is compatible with elastic substrates. In this work, UV-curable and polyimide masks were used to pattern sprayed liquid metal (LM). The effect of the spraying parameters on the thickness and conductivity of the LM was characterized. A minimum LM linewidth of 48 µm was achieved, along with a minimum gap width of 34 µm. A LM patch antenna and transmission line, which can potentially be used for communication systems, were demonstrated using this fabrication process.

One-Step Fabrication of Bio-Compatible Coordination Complex Film on Diverse Substrates for Ternary Flexible Memory

Recently, resistance random access memories (RRAMs) have been studied extensively, because the demand for information storage is increasing. However, it remains challenging to obtain a flexible device because the active materials involved need to be nontoxic, nonpolluting, distortion-tolerable, and biodegradable as well adhesive to diverse flexible substrates. In this paper, tannic acid (TA) and an iron ion (Fe^III ) coordination complex were employed as the active layer in a sandwich-like (Al/active layer/substrate) device to achieve memory performance. A nontoxic, biocompatible TA-Fe^III coordination complex was synthesized by a one-step self-assembly solution method. The retention time of the TA-Fe^III memory performance was up to 15 000 s, the yield up to 53 %. Furthermore, the TA-Fe^III coordination complex can form a high-quality film and shows stable ternary memory behavior on various flexible substrates, such as polyethylene terephthalate (PET), polyimide (PI), printer paper, and leaf. The device can be degraded by immersing it in vinegar solution. Our work will broaden the application of organic coordination complexes in flexible memory devices with diverse substrates.

The design, fabrication, and applications of flexible biosensing devices

Flexible biosensors form part of a rapidly growing research field that take advantage of a multidisciplinary approach involving materials, fabrication and design strategies to be able to function at biological interfaces that may be soft, intrinsically curvy, irregular, or elastic. Numerous exciting advancements are being proposed and developed each year towards applications in healthcare, fundamental biomedical research, food safety and environmental monitoring. In order to place these developments in perspective, this review is intended to present an overview on field of flexible biosensor development. We endeavor to show how this subset of the broader field of flexible and wearable devices presents unique characteristics inherent in their design. Initially, a discussion on the structure of flexible biosensors is presented to address the critical issues specific to their design. We then summarize the different materials as substrates that can resist mechanical deformation while retaining their function of the bioreceptors and active elements. Several examples of flexible biosensors are presented based on the different environments in which they may be deployed or on the basis of targeted biological analytes. Challenges and future perspectives pertinent to the current and future stages of development are presented. Through these summaries and discussion, this review is expected to provide insights towards a systematic and fundamental understanding for the fabrication and utilization of flexible biosensors, as well as inspire and improve designs for smart and effective devices in the future.

Organic and hybrid resistive switching materials and devices

This review presents a timely and comprehensive summary of organic and hybrid materials for nonvolatile resistive switching memory applications in the “More than Moore” era, with particular attention on their designing principles for electronic property tuning and flexible memory performance.