Showing papers on "Flexible electronics published in 2022"

Advances in flexible organic field-effect transistors and their applications for flexible electronics

Abstract: Abstract Flexible electronics have suggested tremendous potential to shape human lives for more convenience and pleasure. Strenuous efforts have been devoted to developing flexible organic field-effect transistor (FOFET) technologies for rollable displays, bendable smart cards, flexible sensors and artificial skins. However, these applications are still in a nascent stage for lack of standard high-performance material stacks as well as mature manufacturing technologies. In this review, the material choice and device design for FOFET devices and circuits, as well as the demonstrated applications are summarized in detail. Moreover, the technical challenges and potential applications of FOFETs in the future are discussed.

Two‐dimensional MXenes : New frontier of wearable and flexible electronics

Abstract: Wearable electronics offer incredible benefits in mobile healthcare monitoring, sensing, portable energy harvesting and storage, human-machine interactions, etc., due to the evolution of rigid electronics structure to flexible and stretchable devices. Lately, transition metal carbides and nitrides (MXenes) are highly regarded as a group of thriving two-dimensional nanomaterials and extraordinary building blocks for emerging flexible electronics platforms because of their excellent electrical conductivity, enriched surface functionalities, and large surface area. This article reviews the most recent developments in MXene-enabled flexible electronics for wearable electronics. Several MXene-enabled electronic devices designed on a nanometric scale are highlighted by drawing attention to widely developed nonstructural attributes, including 3D configured devices, textile and planer substrates, bioinspired structures, and printed materials. Furthermore, the unique progress of these nanodevices is highlighted by representative applications in healthcare, energy, electromagnetic interference (EMI) shielding, and humanoid control of machines. The emerging prospects of MXene nanomaterials as a key frontier in next-generation wearable electronics are envisioned and the design challenges of these electronic systems are also discussed, followed by proposed solutions.

Intrinsically stretchable electronics with ultrahigh deformability to monitor dynamically moving organs

Abstract: Intrinsically stretchable electronics represent an attractive platform for next-generation implantable devices by reducing the mechanical mismatch and the immune responses with biological tissues. Despite extensive efforts, soft implantable electronic devices often exhibit an obvious trade-off between electronic performances and mechanical deformability because of limitations of commonly used compliant electronic materials. Here, we introduce a scalable approach to create intrinsically stretchable and implantable electronic devices featuring the deployment of liquid metal components for ultrahigh stretchability up to 400% tensile strain and excellent durability against repetitive deformations. The device architecture further shows long-term stability under physiological conditions, conformal attachments to internal organs, and low interfacial impedance. Successful electrophysiological mapping on rapidly beating hearts demonstrates the potential of intrinsically stretchable electronics for widespread applications in health monitoring, disease diagnosis, and medical therapies.

Room-temperature high-precision printing of flexible wireless electronics based on MXene inks

Abstract: Abstract Wireless technologies-supported printed flexible electronics are crucial for the Internet of Things (IoTs), human-machine interaction, wearable and biomedical applications. However, the challenges to existing printing approaches remain, such as low printing precision, difficulty in conformal printing, complex ink formulations and processes. Here we present a room-temperature direct printing strategy for flexible wireless electronics, where distinct high-performance functional modules (e.g., antennas, micro-supercapacitors, and sensors) can be fabricated with high resolution and further integrated on various flat/curved substrates. The additive-free titanium carbide (Ti 3 C 2 T x ) MXene aqueous inks are regulated with large single-layer ratio (>90%) and narrow flake size distribution, offering metallic conductivity (~6, 900 S cm −1 ) in the ultrafine-printed tracks (3 μm line gap and 0.43% spatial uniformity) without annealing. In particular, we build an all-MXene-printed integrated system capable of wireless communication, energy harvesting, and smart sensing. This work opens a door for high-precision additive manufacturing of printed wireless electronics at room temperature.

Flexible electronics based on 2D transition metal dichalcogenides

Abstract: We have reviewed recently reported TMD-based flexible devices with their merits and future challenges, which may provide innovative ideas for the enhancements of both device efficiency and flexibility of the TMD-based flexible electronics.

Strain‐Driven Auto‐Detachable Patterning of Flexible Electrodes

Abstract: Flexible electrodes that are multilayer, multimaterial, and conformal are pivotal for multifunctional wearable electronics. Traditional electronic circuits manufacturing requires substrate‐supported transfer printing, which limits their multilayer integrity and device conformability on arbitrary surfaces. Herein, a “shrinkage‐assisted patterning by evaporation” (SHAPE) method is reported, by employing evaporation‐induced interfacial strain mismatch, to fabricate auto‐detachable, freestanding, and patternable electrodes. The SHAPE method utilizes vacuum‐filtration of polyaniline/bacterial cellulose (PANI/BC) ink through a masked filtration membrane to print high‐resolution, patterned, and multilayer electrodes. The strong interlayer hydrogen bonding ensures robust multilayer integrity, while the controllable evaporative shrinking property of PANI/BC induces mismatch between the strains of the electrode and filtration membrane at the interface and thus autodetachment of electrodes. Notably, a 500‐layer substrateless micro‐supercapacitor fabricated using the SHAPE method exhibits an energy density of 350 mWh cm−2 at a power density of 40 mW cm−2, 100 times higher than reported substrate‐confined counterparts. Moreover, a digital circuit fabricated using the SHAPE method functions stably on a deformed glove, highlighting the broad wearable applications of the SHAPE method.

Fully Printed Stretchable and Multifunctional E-Textiles for Aesthetic Wearable Electronic Systems.

Abstract: Electronic textiles (e-textiles) that combine the wearing comfort of textiles and the functionality of soft electronics are highly demanded in wearable applications. However, fabricating robust high-performance stretchable e-textiles with good abrasion resistance and high-resolution aesthetic patterns for high-throughput manufacturing and practical applications remains challenging. Herein, the authors report a new multifunctional e-textile fabricated via screen printing of the water-based silver fractal dendrites conductive ink. The as-fabricated e-textiles spray-coated with the invisible waterproofing agent exhibit superior flexibility, water resistance, wearing comfort, air permeability, and abrasion resistance, achieving a low sheet resistance of 0.088 Ω sq-1 , high stretchability of up to 154%, and excellent dynamic stability for over 1000 cyclic testing (ε = 100%). The printed e-textiles can be explored as strain sensors and ultralow voltage-driven Joule heaters driven for personalized thermal management. They finally demonstrate an integrated aesthetic smart clothing made of their multifunctional e-textiles for human motion detection and body-temperature management. The printed e-textiles provide new opportunities for developing novel wearable electronics and smart clothing for future commercial applications.

Hydrogel‐Based Flexible Electronics

Abstract: Flexible electronics is an emerging field of research involving multiple disciplines, which include but not limited to physics, chemistry, materials science, electronic engineering, and biology. However, the broad applications of flexible electronics are still restricted due to several limitations, including high Young's modulus, poor biocompatibility, and poor responsiveness. Innovative materials aiming for overcoming these drawbacks and boost its practical application is highly desirable. Hydrogel is a class of 3D crosslinked hydrated polymer networks, and its exceptional material properties render it as a promising candidate for the next generation of flexible electronics. Here, the latest methods of synthesizing advanced functional hydrogels and the state‐of‐art applications of hydrogel‐based flexible electronics in various fields are reviewed. More importantly, the correlation between properties of the hydrogel and device performance is discussed here, to have better understanding of the development of flexible electronics by using environmentally responsive hydrogels. Last, perspectives on the current challenges and future directions in the development of hydrogel‐based multifunctional flexible electronics are provided.

Recent Progress in Printed Physical Sensing Electronics for Wearable Health-Monitoring Devices: A Review

Abstract: Printed electronics (PEs), as a fast-growing advanced manufacturing technology in recent years, plays an essential role in development of wearable electronic sensors, flexible displays, human-machine interaction, and thin electronics owing to its low cost, high throughput, and the possibility to be fabricated on diverse thin substrates with good flexibility and stretchability. Various PEs have been developed, such as physical sensing devices, electrochemical sensors, wearable supercapacitors and energy harvesters, stretchable electrodes, thin-film transistors (TFTs), and printed transceiving circuits. In this work, recent progress on physical sensing devices and their interface circuits developed by the printing process are reviewed in terms of their functions, printing methods, materials, and performance. The printed physical sensors used for monitoring the basic biometric parameters through physical sensing mechanisms, such as temperature sensors for skin temperature, pressure sensors for human pulse wave, strain sensors for human motions, biopotential electrodes for electrocardiogram signals, and multiple-function physical sensing platforms, have been studied and highlighted with their good designs and advanced materials. The state-of-the-art printed interface circuits for the wearable sensors such as interconnects, TFTs, digital circuits, amplifiers, oscillators, and antennas have been reviewed in terms of their structures and functions from basic to advanced levels. The challenge and suggestions of the printed wearable devices for future developments are discussed and end with a conclusion.

Novel, Flexible, and Transparent Thin Film Polyimide Aerogels with Enhanced Thermal Insulation and High Service Temperature

Abstract: Due to their high service temperature, excellent thermal insulation, nanoporous morphology, and low dielectric constant, polyimide (PI) aerogels have potential capability to be used in the next generation of microelectronic...

Healable, Recyclable, and Multifunctional Soft Electronics Based on Biopolymer Hydrogel and Patterned Liquid Metal.

Abstract: Recent years have witnessed the rapid development of sustainable materials. Along this line, developing biodegradable or recyclable soft electronics is challenging yet important due to their versatile applications in biomedical devices, soft robots, and wearables. Although some degradable bulk hydrogels are directly used as the soft electronics, the sensing performances are usually limited due to the absence of distributed conducting circuits. Here, sustainable hydrogel-based soft electronics (HSE) are reported that integrate sensing elements and patterned liquid metal (LM) in the gelatin-alginate hybrid hydrogel. The biopolymer hydrogel is transparent, robust, resilient, and recyclable. The HSE is multifunctional; it can sense strain, temperature, heart rate (electrocardiogram), and pH. The strain sensing is sufficiently sensitive to detect a human pulse. In addition, the device serves as a model system for iontophoretic drug delivery by using patterned LM as the soft conductor and electrode. Noncontact detection of nearby objects is also achieved based on electrostatic-field-induced voltage. The LM and biopolymer hydrogel are healable, recyclable, and degradable, favoring sustainable applications and reconstruction of the device with new functions. Such HSE with multiple functions and favorable attributes should open opportunities in next-generation electronic skins and hydrogel machines.

High Operation Frequency and Strain Tolerance of Fully Printed Oxide Thin Film Transistors and Circuits on PET Substrates.

Abstract: The major limitations of solution-processed oxide electronics include high process temperatures and the absence of necessary strain tolerance that would be essential for flexible electronic applications. Here, a combination of low temperature (<100 °C) curable indium oxide nanoparticle ink and a conductive silver nanoink, which are used to fabricate fully-printed narrow-channel thin film transistors (TFTs) on polyethylene terephthalate (PET) substrates, is proposed. The metal ink is printed onto the In2 O3 nanoparticulate channel to narrow the effective channel lengths down to the thickness of the In2 O3 layer and thereby obtain near-vertical transport across the semiconductor layer. The TFTs thus prepared show On/Off ratio ≈106 and simultaneous maximum current density of 172 µA µm-1 . Next, the depletion-load inverters fabricated on PET substrates demonstrate signal gain >200 and operation frequency >300 kHz at low operation voltage of VDD = 2 V. In addition, the near-vertical transport across the semiconductor layer is found to be largely strain tolerant with insignificant change in the TFT and inverter performance observed under bending fatigue tests performed down to a bending radius of 1.5 mm, which translates to a strain value of 5%. The devices are also found to be robust against atmospheric exposure when remeasured after a month.

Directional Freezing Assisted 3D Printing to Solve a Flexible Battery Dilemma: Ultrahigh Energy/Power Density and Uncompromised Mechanical Compliance

Abstract: Flexible lithium‐ion batteries (LIBs) have been in the spotlight with the booming development of flexible/wearable electronics. However, the dilemma of simultaneously balancing excellent energy density with mechanical compliance in flexible electrodes impedes their practical applications. Here, for the first time, a directional freezing assisted 3D printing strategy is proposed to construct flexible, compressible, and ultrahigh energy/power density LIBs. Cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) are entangled with each other to form an interwoven network and uniformly wrap the active materials, ensuring fast electron transfer and stress release through the entire printed electrode. Furthermore, vertical channels induced by directional freezing can act as high‐speed ion diffusion paths, which effectively solve the sluggish ion transport limitation of flexible 3D printed electrodes as the mass loading increases. As expected, the 3D printed LIB delivers a record‐high energy density (15.2 mWh cm–2) and power density (75.9 mW cm–2), outperforming all previously reported flexible LIBs. Meanwhile, the printed flexible full LIBs maintains favorable electrochemical stability in both bending and compression states. This work suggests a feasible avenue for the design of LIBs that resolves the long‐standing issue of high electrochemical performance and mechanical deformation in wearable and smart electronics.

A soft and stretchable electronics using laser-induced graphene on polyimide/PDMS composite substrate

Abstract: Abstract The one-step fabricated laser-induced graphene (LIG) has the advantages of low cost, patterning of various desired geometries, and high sensitivity. However, the robustness of substrates imposes certain constraints on their applications in stretchable devices. In this paper, the substrate composed of polydimethylsiloxane (PDMS) and polyimide (PI) particles is proposed to serve as the platform to manufacture LIG. Ascribing to the inherent soft and stretchable attributes of the PI/PDMS composite substrate, the LIG-based sensors can fit complex 3D configurations or bear a mechanical tension over 15%. Notably, the fluence of the laser is experimentally and theoretically determined as the only principle to characterize the formation of conductive LIG on PI/PDMS composite greatly facilitating the selection of the allowable laser scanning parameters to form the desired LIG-based devices. Three demonstrations are conducted to highlight the superiority and the potential of this soft and stretchable LIG-based system in wearable electronics and soft robots.

Prospects and Challenges of Flexible Stretchable Electrodes for Electronics

Abstract: The application of flexible electronics in the field of communication has made the transition from rigid physical form to flexible physical form. Flexible electrode technology is the key to the wide application of flexible electronics. However, flexible electrodes will break when large deformation occurs, failing flexible electronics. It restricts the further development of flexible electronic technology. Flexible stretchable electrodes are a hot research topic to solve the problem that flexible electrodes cannot withstand large deformation. Flexible stretchable electrode materials have excellent electrical conductivity, while retaining excellent mechanical properties in case of large deformation. This paper summarizes the research results of flexible stretchable electrodes from three aspects: material, process, and structure, as well as the prospects for future development.

Flexible and wearable strain sensors based on conductive hydrogels

Abstract: In recent years, the field of flexible electronics has been thriving in academic achievements. Among them, the hydrogel-based strain sensors possess some characteristic advantages in stretchability, flexibility, stickiness and regulable modulus of elasticity, thus they are more likely to attach to human skin and the surfaces of objects. Compared to traditional sensors, hydrogels can overcome shortcomings in toughness and elasticity. Therefore, hydrogels are suitable to serve as the core materials of wearable electronics. Hydrogel-based strain sensors, as a typical kind of hydrogel flexible electronics, are in the categories of resistance sensors and capacitive sensors, which are primarily used for real-time monitoring of human motions. This review mainly introduces the up-to-date relative literatures in the field of hydrogel-based strain sensors.

Dual‐Channel Flexible Strain Sensors Based on Mechanofluorescent and Conductive Hydrogel Laminates

Abstract: Flexible strain sensors are of great importance in many emerging applications for human motion monitoring, implanted devices, and human–machine interactive systems. However, the dual‐channel sensing systems that enable both strain‐dependent electronic and visually optical signal responses still remain underdeveloped, but such systems are of great interest for human–machine interactive uses. Here, inspired by the mechanically modulated skin color changes of squids via muscle contracting/releasing movements, a class of mechanofluorescent and conductive hydrogel laminates for visually flexible electronics is presented. The sensing laminates consist of interfacially bonded red fluorescent hydrogel, polydimethylsiloxane and carbon nanotubes (CNTs) film. Since the densely stacked microscopic CNTs film can be precisely stretched to induce the formation of network microcracks, the developed hydrogel laminates are endowed with simultaneous fluorescence‐color and resistance changes, which can function as dual‐channel flexible sensors for real‐time human motion monitoring. These properties make the bioinspired soft hydrogel laminate electronics quite promising in the flexible electronics field.

Ultrathin Hydrogel Films toward Breathable Skin‐Integrated Electronics

Abstract: On‐skin electronics that offer revolutionary capabilities in personalized diagnosis, therapeutics, and human–machine interfaces require seamless integration between the skin and electronics. A common question remains whether an ideal interface can be introduced to directly bridge thin‐film electronics with the soft skin, allowing the skin to breathe freely and the skin‐integrated electronics to function stably. Here, an ever‐thinnest hydrogel is reported that is compliant to the glyphic lines and subtle minutiae on the skin without forming air gaps, produced by a facile cold‐lamination method. The hydrogels exhibit high water‐vapor permeability, allowing nearly unimpeded transepidermal water loss and free breathing of the skin underneath. Hydrogel‐interfaced flexible (opto)electronics without causing skin irritation or accelerated device performance deterioration are demonstrated. The long‐term applicability is recorded for over one week. With combined features of extreme mechanical compliance, high permeability, and biocompatibility, the ultrathin hydrogel interface promotes the general applicability of skin‐integrated electronics.

Mechanically Ultra-Robust, Elastic, Conductive, and Multifunctional Hybrid Hydrogel for a Triboelectric Nanogenerator and Flexible/Wearable Sensor.

Abstract: Flexibility/wearable electronics such as strain/pressure sensors in human-machine interactions (HMI) are highly developed nowadays. However, challenges remain because of the lack of flexibility, fatigue resistance, and versatility, leading to mechanical damage to device materials during practical applications. In this work, a triple-network conductive hydrogel is fabricated by combining 2D Ti3 C2 Tx nanosheets with two kinds of 1D polymer chains, polyacrylamide, and polyvinyl alcohol. The Ti3 C2 Tx nanosheets act as the crosslinkers, which combine the two polymer chains of PAM and PVA via hydrogen bonds. Such a unique structure endows the hydrogel (MPP-hydrogel) with merits such as mechanical ultra-robust, super-elasticity, and excellent fatigue resistance. More importantly, the introduced Ti3 C2 Tx nanosheets not only enhance the hydrogel's conductivity but help form double electric layers (DELs) between the MXene nanosheets and the free water molecules inside the MPP-hydrogel. When the MPP-hydrogel is used as the electrode of the triboelectric nanogenerator (MPP-TENG), due to the dynamic balance of the DELs under the initial potential difference generated from the contact electrification as the driving force, an enhanced electrical output of the TENG is generated. Moreover, flexible strain/pressure sensors for tiny and low-frequency human motion detection are achieved. This work demonstrates a promising flexible electronic material for e-skin and HMI.

In Tandem Contact‐Transfer Printing for High‐Performance Transient Electronics

Abstract: High‐performance flexible electronics developed with resource efficient printing route will transform the way future electronics is manufactured and used to advance applications such as healthcare, Internet of Things, wearables, consumer electronics, etc. Herein, an innovative approach is presented that involves, for the first time, the in‐tandem use of contact and transfer printing methods to realize high‐quality electronic layers at selected locations on rigid (Si/SiO2), flexible (polyimide), and biodegradable (magnesium (Mg) foils). Superior grade quality of printed electronic layers is demonstrated by realizing transistors and printed UV photodetectors (PDs) employing high‐resolution electrohydrodynamic printing. The all‐printed PDs show extremely high performance for UV detection, with extraordinary high responsivity (>107 A W−1) and specific detectivity (≈1017 Jones) values at low UV intensity of 0.1 µW cm−2. Finally, the fabricated PDs on Mg foil are dissolved in deionized water at room temperature. Thus, in‐tandem contact and transfer printing has potential for ecofriendly development of transient electronics. Further, the approach allows printing of wide range of nanomaterials and heterostructures or complex superlattice structures, which can open exciting new possibilities for high‐performance electronics.