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Given the advancements in modern living standards and technological development, conventional smart devices have proven inadequate in meeting the demands for a high-quality lifestyle. Therefore, a revolution is necessary to overcome this impasse and facilitate the emergence of flexible electronics. Specifically, there is a growing focus on health detection, necessitating advanced flexible preparation technology for biosensor-based smart wearable devices. Nowadays, numerous flexible products are available on the market, such as electronic devices with flexible connections, bendable LED light arrays, and flexible radio frequency electronic tags for storing information. The manufacturing process of these devices is relatively straightforward, and their integration is uncomplicated. However, their functionality remains limited. Further research is necessary for the development of more intricate applications, such as intelligent wearables and energy storage systems. Taking smart wear as an example, it is worth noting that the current mainstream products on the market primarily consist of bracelet-type health testing equipment. They exhibit limited flexibility and can only be worn on the wrist for measurement purposes, which greatly limits their application diversity. Flexible energy storage and flexible display also face the same problem, so there is still a lot of room for development in the field of flexible electronics manufacturing. In this review, we provide a brief overview of the developmental history of flexible devices, systematically summarizing representative preparation methods and typical applications, identifying challenges, proposing solutions, and offering prospects for future development.

Roll-to-roll (R2R) manufacturing is an important manufacturing technology platform used extensively for mass-producing a host of film-type products in several traditional industries such as printing, silver-halide photography, and paper. Over the last two decades, some of the methodologies and know-how of R2R manufacturing have been extended and adapted in many new technology areas, including microelectronics, display, photovoltaics, and microfluidics. This comprehensive book presents the state-of-the-art unit operations of the R2R manufacturing technology, providing a practical resource for scientists, engineers, and practitioners not familiar with the fundamentals of R2R technology. This book reviews new developments in areas such as flexible glass, display, and photovoltaics and covers a number of process innovations implemented recently to extend and improve the capabilities of traditional R2R lines. It covers such topics as: coating and solidification processes, in-line vacuum deposition, drying, web handling and winding, polymer film substrates, novel hybrid composite films, flexible solar cells and more.

Printed electronics are a set of additive manufacturing methods for creating future flexible electronics on thin polymeric sheets. We proposed the toner-type, dry, page-printing of Ag–Ni composite conductive particles on flexible plastic sheets without pre-treatment. No chemical solvents are necessary to compose the inks of the electronic materials used for the toner-type printing, and no chemical treatment is required for the plastic film substrate surface. In addition, multilayer printing is simple when using toner printing because previously printed materials do not need to be resolved; furthermore, composing the thick films of the electronic materials is relatively simple. In this study, we fabricated an Ag–Ni composite toner to improve the fluidity of the toner particles compared to bare Ag particles. We successfully printed IC peripheral circuits at a resolution of 0.20 mm and demonstrated that the actual electrical circuit pattern can be formed using our method.

Low-temperature activation of oxide semiconductor materials such as In-Ga-Zn-O (IGZO) is a key approach for their utilization in flexible devices. We previously reported that the activation temperature can be reduced to 150 °C by hydrogen-doped IGZO (IGZO:H), demonstrating a strong potential of this approach. In this paper, we investigated the mechanism for reducing the activation temperature of the IGZO:H films. In situ Hall measurements revealed that oxygen diffusion from annealing ambient into the conventional Ar/O2-sputtered IGZO film was observed at >240 °C. Moreover, the temperature at which the oxygen diffusion starts into the film significantly decreased to 100 °C for the IGZO:H film deposited at hydrogen gas flow ratio (R[H2]) of 8%. Hard X-ray photoelectron spectroscopy indicated that the near Fermi level (EF) defects in the IGZO:H film after the 150 °C annealing decreased in comparison to that in the conventional IGZO film after 300 °C annealing. The oxygen diffusion into the film during annealing plays an important role for reducing oxygen vacancies and subgap states especially for near EF. X-ray reflectometry analysis revealed that the film density of the IGZO:H decreased with an increase in R[H2] which would be the possible cause for facilitating the O diffusion at low temperature.

In recent years, to meet the greater demand for next generation electronic devices that are transplantable, lightweight and portable, flexible and large-scale integrated electronics attract much more attention have been of interest in both industry and academia. Organic electronics and stretchable inorganic electronics are the two major branches of flexible electronics. With the semiconductive and flexible properties of the organic semiconductor materials, flexible organic electronics have become a mainstay of our technology. Compared to organic electronics, stretchable and flexible inorganic electronics are fabricated via mechanical design with inorganic electronic components on flexible substrates, which have stretchability and flexibility to enable very large deformations without degradation of performance. This review summarizes the recent progress on fabrication strategies, such as hydrodynamic organic nanowire printing and inkjet-assisted nanotransfer printing of flexible organic electronics, and screen printing, soft lithography and transfer printing of flexible inorganic electronics. In addition, this review considers large-scale organic and inorganic flexible electronic systems and the future applications of flexible and stretchable electronics.

The need for flexible electronics with outstanding bending properties is increasing due to the demand for wearable devices and next-generation flexible or rollable smartphones. In addition, the requirements for flexible or rigid–flexible electronics are sharply increasing to achieve the design of space-saving electronic devices. In this regard, coverlay (CL) film is a key material used in the bending area of flexible electronics, albeit infrequently. Because flexible electronics undergo folding and unfolding numerous times, CL films with superior mechanical and bending properties are required so that the bending area can endure such severe stress. However, because current CL films are only used for a designated bending area in the flexible electronics panel, their highly complicated and expensive manufacturing procedure is a disadvantage. In addition, the thickness of CL films must be decreased to satisfy the ongoing requirement for increasingly thin products. However, due to the limitations of the two-layer structure of existing CL films, the manufacturing process cannot be made more cost effective by simply applying more thin film onto the board. To address this problem, we have developed liquid coverlay inks (LCIs) with superior bendable properties, in comparison with CL films, when applied onto flexible electronics using a screen-printing method. The results show that LCIs have the potential to become one of the leading candidates to replace existing CL films because of their lower cost and faster manufacturing process.

A resistive switching behaviour of printed, flexible Cu/CuO/(AgO)/Ag memristor devices is demonstrated for the first time. It is suggested that the high resistance state and low resistance state of bipolar resistive switching behaviour are governed by the migration of oxygen between the copper oxide and silver oxide layers. The devices have characteristics of inexpensive low-temperature fabrication, low-power operation and no required electroforming process. Ink-jet printing was used to fabricate the devices on polymer substrates. Since these devices are fabricated on flexible polyimide, they have compatibility with flexible electronic technologies.

Highly conductive ink with low sintering temperature is important for printed electronics on paper substrate. Silver nanoparticles (Ag NPs) of different average radii ranging from 48 to 176 nm were synthesized by adjusting the Ag + concentration in the reaction process. The electric resistivity of the Ag NP-based ink film in relation to Ag NP size, sintering temperature, amount of PVP capping agent on Ag NP surface, and morphology evolution of the film during heating process was investigated. It was found that the resistivity of the films reduced very rapidly with increasing particle size due above all to reduced amount of protective agent capping on the Ag NPs. A semi-empirical relationship between the resistivity and the particle size was proposed. With the help of this mathematical expression, one gains both systematic and detailed insight to the resistivity evaluation with regard to the Ag particle size. The optimal electric resistivity of 4.6 μΩ cm was achieved at 140 °C for 10 min which was very close to the resistivity value of bulk Ag (1.58 μΩ cm). Mechanical flexibility of the printed electronics with the Ag NP-based ink on paper substrates was investigated. The prints on the art coated paper exhibited better flexibility compared to that on the photopaper. This might be attributed to the surface coating composition, surface morphology of the paper, and their corresponding ink absorption property.

We fabricate a wearable blood leakage sensor on a cotton textile by combining two newly developed techniques. First, we employ a screen-offset printing technique that avoids blurring, short circuiting between adjacent conductive patterns, and electrode fracturing to form an interdigitated electrode structure for the sensor on a textile. Furthermore, we develop a scheme to distinguish blood from other substances by utilizing the specific dielectric dispersion of blood observed in the sub-megahertz frequency range. The sensor can detect blood volumes as low as 15 μL, which is significantly lower than those of commercially available products (which can detect approximately 1 mL of blood) and comparable to a recently reported value of approximately 10 μL. In this study, we merge two technologies to develop a more practical skin-friendly sensor that can be applied for safe, stress-free blood leakage monitoring during hemodialysis.

Flexible wearables have attracted extensive interests for personal human motion sensing, intelligent disease diagnosis, and multifunctional electronic skins. However, the reported flexible sensors, mostly exhibited narrow detection range, low sensitivity, limited degradability to aggravate environmental pollution from vast electronic wastes, and poor antibacterial performance to hardly improve skin discomfort and skin inflammation from bacterial growth under long‐term wearing. Herein, bioinspired from human skin featuring highly sensitive tactile sensation with spinous microstructures for amplifying sensing sensitivity between epidermis and dermis, a wearable antibacterial degradable electronics is prepared from degradable elastomeric substrate with MXene‐coated spinous microstructures templated from lotus leaf assembled with the interdigitated electrode. The degradable elastomer is facilely obtained with tunable modulus to match the modulus of human skin with improved hydrophilicity for rapid degradation. The as‐obtained sensor displays ultra‐low detection limit (0.2 Pa), higher sensitivity (up to 540.2 kPa−1), outstanding cycling stability (>23,000 cycles), a wide detection range, robust degradability, and excellent antibacterial capability. Facilitated by machine learning, the collected sensing signals from the integrated sensors on volunteer's fingers to the related American Sign Language are effectively recognized with an accuracy up to 99%, showing excellent potential in wireless human movement sensing and smart machine learning‐enabled human–machine interaction. A skin bionic antibacterial degradable electronics is facilely fabricated from MXene‐coated convex spinous microstructures‐contained degradable elastomeric film with surface spinosum microstructures templated from lotus leaf assembled with interdigitated electrode. It demonstrates ultrahigh sensitivity (540.2 kPa−1), low sensing limit (0.2 Pa), excellent cycling stability (over 23000 cycles), robust degradability and antibacterial capability for ultrasensitive diagnostic monitoring and intelligent human–interactive sensing.