Intrinsically Photopatternable High‐k Polymer Dielectric for Flexible Electronics

The InGaZnO thin films with varied the O2 flow ratios were deposited by a magnetron sputtering system. The effect of O2 content on the structure, surface morphology, optical and electrical properties of InGaZnO thin films is studied. Then, we investigate the relationship between bias stress stability and density of states (DOS) of thin film transistors (TFTs) with various oxygen partial pressure InGaZnO (IGZO) as the channel layer. The temperature-dependent field-effect measurements are used to calculate DOS of IGZO TFTs. With the increase of the oxygen partial pressure, the value of DOS decreases from 2.2 × 1016 to 5.5 × 1015 cm-3. Moreover, the positive gate bias stress of IGZO TFTs are investigated. Under positive gate bias stress, the transfer curves of IGZO TFTs with various oxygen partial pressure show an obvious shift, the value of threshold voltage shift () is 5.1, 2.94, 2 and 0.8 V, respectively. The results suggest that the device with a smaller DOS is more stable than others. Therefore, this study offers a brief and accurate method to demonstrate instability mechanism of IGZO TFTs.

With the rapid development of wearable devices, flexible sensors, and flexible displays, higher performance requirements are being placed on conductive materials used in flexible electronic devices. Conductive polymers, known for their excellent flexibility, good conductivity, and tunable molecular structures, have become a research hotspot in the field of flexible electronics. This paper systematically summarizes the design and synthesis strategies of conductive polymers for flexible electronic devices, with a focus on the synthesis methods and structural regulation techniques of typical conductive polymers such as polyaniline (PANI), polypyrrole (PPy), and poly(3,4-ethylenedioxythiophene) (PEDOT). It further analyzes their electrical properties, mechanical performance, and environmental stability in flexible electronics. Finally, the paper discusses future development trends and challenges of conductive polymers in flexible devices, aiming to provide a theoretical foundation and technical support for the research of high-performance flexible electronic materials.

Modern information technologies have tremendous demands on flexible electronic devices such as thin-film transistors (TFTs). As the flexible TFT technology continues to advance, the properties of the gate dielectric become a bottleneck for the flexible TFTs to achieve fast switching speed, low operation voltage, and downscaling. The gate dielectric layer should be sufficiently thin, insulating, and flexible, and therefore, hybrid organic–inorganic dielectrics are of great promise for this purpose. In this work, we develop a scalable vapor-phase MLD/ALD technique, which combines molecular layer deposition (MLD) and atomic layer deposition (ALD), to grow a new hybrid polymer–oxide dielectric thin-film material of polyimide (PI) and Al2O3, and demonstrate that the afforded hybrid polyimide–Al2O3 (HPA) films are well suited as the bendable gate dielectrics for flexible electronic applications. We also perform mechanism investigation on the growth of PI and Al2O3 during the MLD/ALD HPA process and find that the growth of PI is strongly affected by the Al2O3 surface and therefore exhibits a two-stage behavior. We further evaluate the electrical and bending performances of the afforded HPA dielectrics and apply the HPA films as the gate dielectrics for flexible carbon-nanotube TFTs. The fabricated TFTs can well withstand 1000-time repetitive bending without an increase in the TFT gate leakage current, which shows the high promise of the HPA dielectrics for flexible electronic applications. Considering that the MLD/ALD fabrication approach is advantageous for high process reproducibility and large-scale compatibility, we envision that the MLD/ALD-prepared HPA dielectrics will have great applications in future complex flexible electronic circuits.

Fabrication of self-recoverable flexible and stretchable electronic devices

Thin film transistors (TFTs) with amorphous InGaZnO (IGZO) channel layer were fabricated by radio frequency magnetron sputtering technique. The IGZO films show optical transparency over 80 % both before annealing and after annealing. It was found that performances of transistors with IGZO thin films annealed in air at 450 °C were significantly improved. Through annealing treatment, Saturation current of TFTs increased from 2.8 to 181 μA at bias of VDS = 20, VGS = 20 V, and saturation mobility is up from 1.49 to 15.8 cm2 V−1 s−1. In addition, X-ray photoelectric spectroscopy (XPS) was performed to provide elemental information on the surface of the IGZO films before and after annealing. O1s XPS spectra of unannealed and annealed IGZO films indicated oxygen vacancy concentration decreased by annealing treatment.

In recent years, flexible electronic devices have become a hot topic of scientific research. These flexible devices are the basis of flexible circuits, flexible batteries, flexible displays and electronic skins. Graphene-based materials are very promising for flexible electronic devices, due to their high mobility, high elasticity, a tunable band gap, quantum electronic transport and high mechanical strength. In this article, we review the recent progress of the fabrication process and the applications of graphene-based electronic devices, including thermal acoustic devices, thermal rectifiers, graphene-based nanogenerators, pressure sensors and graphene-based light-emitting diodes. In summary, although there are still a lot of challenges needing to be solved, graphene-based materials are very promising for various flexible device applications in the future.

In this study, we report a novel vertical diffusion method for fabricating solution-processed quaternary In-Ga-Zn-O (IGZO) (defined as vd-IGZO) thin-film transistors (TFTs). Compared with conventional IGZO (defined as con-IGZO) TFT annealed at 380°C, vd-IGZO thin film is to spin coat Ga2O3, ZnO and In2O3 binary oxide precursors consecutively and then anneal at 250°C. Finally, the IGZO film with a vertically gradient Ga, Zn, In diffusion is obtained and used as the channel layer of TFTs. The results showed that the novel method lead to an improvement in charge carrier mobility and an improvement in the on-off current ratio of IGZO TFTs along with an improved stability. Compared with those for con-IGZO TFTs, the mobility for vd-IGZO TFT reaches 2.81cm2 V−1 s−1 from 0.88cm2 V−1 s−1, the threshold voltage(Vth) changes from 3.7V to 0.3V, the sub-threshold swing (S.S) decreases from 0.51V/dec to 0.35V/dec, and the on-current/off-current (Ion/Ioff) increases from 2.1 × 106 to 2.3 × 107. Besides, the positive bias stress (PBS), negative bias stress (NBS) and environmental stability are all improved to some extent. Hence this novel vertical diffusion method shows great potential to be applicable in the fabrication of flexible TFT.

Oxide semiconductors have been investigated as channel layers for thin film transistors (TFTs) which enable next-generation devices such as high-resolution liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, flexible electronics, and innovative devices. Here, high-performance and stable Ga-Sn-O (GTO) TFTs were demonstrated for the first time without the use of rare metals such as In. The GTO thin films were deposited using radiofrequency (RF) magnetron sputtering. A high field effect mobility of 25.6 cm2/Vs was achieved, because the orbital structure of Sn was similar to that of In. The stability of the GTO TFTs was examined under bias, temperature, and light illumination conditions. The electrical behaviour of the GTO TFTs was more stable than that of In-Ga-Zn-O (IGZO) TFTs, which was attributed to the elimination of weak Zn-O bonds.

Flexible electronics have inspired many novel and very important applications in recent years and various flexible electronic devices such as diodes, transistors, circuits, sensors, and radiofrequency (RF) passive devices including antennas and inductors have been reported. However, the lack of a high-performance RF resonator is one of the key bottlenecks to implement flexible wireless electronics. In this study, for the first time, a novel ultra-flexible structured film bulk acoustic resonator (FBAR) is proposed. The flexible FBAR is fabricated on a flexible polyimide substrate using piezoelectric thin film aluminum nitride (AlN) for acoustic wave excitation. Both the shear wave and longitudinal wave can be excited under the surface interdigital electrodes configuration we proposed. In the case of the thickness extension mode, a flexible resonator with a working frequency as high as of 5.2325 GHz has been realized. The resonators stay fully functional under bending status and after repeated bending and re-flattening operations. This flexible high-frequency resonator will serve as a key building block for the future flexible wireless electronics, greatly expanding the application scope of flexible electronics.

Synthesis of PVA@S-BNNSs flexible fiber backbone by electrostatic spinning assisting the construction of excellent ductile epoxy thermal interface materials

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.(1) This review focuses on silk fibroin serving as active functional components to construct flexible electronics. (2) Recent representative reports on flexible electronic devices that applied silk fibroin as fundamental supporting components are summarized. (3) This review summarizes the current typical silk fibroin-based materials and the corresponding advanced preparation technologies. (4) The current challenges and future development of silk fibroin-based flexible electronic devices are analyzed.

Flexible electronics have attracted increased attention in advanced fields, such as electronic skin and flexible displays. However, most flexible electronic devices are made with polymers that lack biocompatibility and environmental friendliness. Meanwhile, the complexity of the manufacturing process further restricts the mass production of flexible devices. This study uses biocompatible sodium alginate (SA) derived from seaweed as a flexible substrate to fabricate a thin film transistor (TFT) without using lithography, effectively protecting the flexible substrate from eroding. The flexible TFT with SA substrate can be opened at the Vg of ~ 0 V, and the mobility 26.8 cm2/(V·s) is realized. Flexible TFT with SA substrate has desirable characteristics, such as biocompatibility, transparency, and high mobility, providing promise for advancing the implementation of electronic skin and flexible displays.

This paper investigates the effects of different passivation layers (PVLs) on the electrical performance and reliability of amorphous indium gallium zinc oxide (a-In-Ga-ZnO) thin film transistors (TFTs). By rational design, the fabricated a-InGaZnO TFT with hafnium oxide and aluminum oxide (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) dual PVLs exhibits a field-effect mobility of 13.5 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, low sub threshold swing of 0.32 V/decade, and especially, small threshold voltage shifts of 0.5 (-0.6) V and 1.1 (-1.2) V under positive (negative) gate bias, and light illumination stress at the relative humidity of 40%. Furthermore, the a-In-Ga-ZnO TFTs with HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dual PVLs maintain reasonable mobility and electrical performance even exposure to ambient condition for up to four months. This enhanced stability is attributed to the presence of high-quality HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dual PVLs, which not only could suppress the photodesorption, reduce the total trap density and subgap photoexcitation behavior, but also protect the channel from environmental effects. Thus, the rational-designed HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dual PVLs passivated a-In-Ga-ZnO TFTs with superior reliability represent a great step toward the achievement of long-term reliable zinc oxide-based oxide TFTs.

Flexible and stretchable electronics represent today's cutting-edge electronic technologies. As the most-fundamental component of electronics, the thin-film electrode remains the research frontier due to its key role in the successful development of flexible and stretchable electronic devices. Stretchability, however, is generally more challenging to achieve than flexibility. Stretchable electronic devices demand, above all else, that the thin-film electrodes have the capacity to absorb a large level of strain (>>1%) without obvious changes in their electrical performance. This article reviews the progress in strategies for obtaining highly stretchable thin-film electrodes. Applications of stretchable thin-film electrodes fabricated via these strategies are described. Some perspectives and challenges in this field are also put forward.

High-resolution flexible electronic devices are widely used in the fields of soft robotics, smart human-machine interaction, and intelligent e-healthcare monitoring due to their mechanical flexibility, ductility, and compactness. The electrohydrodynamic jet printing (e-jet printing) technique is used for constructing high-resolution and cross-scale flexible electronic devices such as field-effect transistors (FETs), flexible sensors, and flexible displays. As a result, researchers are paying close attention to e-jet printing flexible electronic devices. In this review, we focused on the latest advancements in high-resolution flexible electronics made by e-jet printing technology, including various materials used in e-jet printing inks, the process control of e-jet printing, and their applications. First, we summarized various functional ink materials available for e-jet printing, including organic, inorganic, and hybrid materials. Then, the interface controlling the progress of e-jet printing was discussed in detail, including the physical and chemical properties of the functional ink, the interfacial wettability between the ink and substrate, and the micro-droplet injection behavior in a high-voltage field. Additionally, various applications of e-jet printing in the fields of flexible electrodes, FETs, flexible sensors, and flexible displays were demonstrated. Finally, the future problems and potential associated with the development of next generation e-jet printing technology for flexible electronic devices were also presented.