Study on the Film-Forming Mechanism of Polymer-Metal Oxide Composite Ink Systems Containing Different Polymer Molecules.

A printable, flexible display panel is an important trend in the field of information display, which requires better mechanical and electrical properties of device materials. Polymer-metal oxide composite materials are promising in the functional layer of a thin-film transistor (TFT) and can be sufficiently fabricated by polymer-metal salt solution systems through the sol-gel process. For the development of polymer-metal oxide composite ink, it is necessary to study the film-forming mechanism of the composite film during solidification, which is an important reference in ink component design. However, the evolution of the composite structure is quite complex, which brings a challenge to characterization and analyzation. We applied a series of characterization methods to study the film-forming process of composite ink from sol to gel and to solid, and an emerging testing technology, nano-infrared spectroscopy (nano-IR), was applied to characterize the gel film. The research conclusion showed that the type of functional group can significantly affect the morphology of the initial particle and can finally determine the microstructure of the composite film. The study provides references for the development of composite ink as well as the characterization method for ink and film with complex composition.

Morphological Regulation of Printed Low-Temperature Conductive Ink.

The unbalanced evaporation of solvents in low-temperature sintered inks for printed electronics leads to a series of problems in the actual printing process, including printed pattern distortion, surface cracking, and the coffee ring effect, which has become a serious obstacle to this technique. Here, we present a comprehensive investigation of the influence of the solvent composition, environmental, and sintering conditions on the complicated pattern formation process of reactive silver inks. The results first showed that only inks with a certain wettability of solvents could form well-defined patterns. Then, the solvent composition and ambient humidity can be adjusted to balance the nonequilibrium evaporative flow within the liquid and thus to obtain a flat liquid film. Combined with the rapid UV sintering process, the particle size, porosity, and roughness could be controlled to produce dense and homogeneous silver films. Finally, we successfully printed silver electrodes with a smooth and dense surface (Rqs ∼ 21 nm in 0.8 × 0.8 mm2 area and less than 1% porosity) under an optimized relative humidity (RH) of 50-60% at room temperature with the solvent composition of IPA (isopropanol)/2,3-BD (2,3-butanediol) = 8:2. In addition, we also demonstrated high-performance Pr-IZO (praseodymium-doped indium-zinc oxide) thin film transistors (TFTs) with a mobility (µsat) of 2.14 cm2/V/s and Ion/Ioff ratio of over 107 using source-drain electrodes printed under optimized conditions.

Binary Solvent Systems for Piezoelectric Printing Crack-Free PAM/ZrOx Hybrid Thin Films through Nanostructure Modulation.

Polymer/oxide hybrid thin films, which have excellent electrical and mechanical performance, can be effectively fabricated through the sol-gel process, showing great potential in the future printed electronics. However, gelation of polymer/oxide ink systems can easily occur during a thermal process in which case capillary stress can lead to the crack of printed films due to the long period of stress accumulation. To solve this problem, the effect of different solvent systems on formed PAM/ZrOx hybrid films, which were printed by piezoelectric printing, was studied in this paper, including single solvent systems of glycol and binary solvent systems of glycol and water. The result showed that the microstructure characteristics and mechanical properties of hybrid nanostructures formed in different solvent systems varied significantly, and crack behavior can be regulated by simply adjusting the water volume ratio of the solvent system. The crack formation was significantly inhibited when the water volume ratio reached 25%.

Functional Metal Oxide Ink Systems for Drop-on-Demand Printed Thin-Film Transistors.

Drop-on-demand printing is a noncontact direct patterning and rapid manufacturing printing technology which shows considerable potential in future display manufacturing. Metal oxides are an important kind of functional material in thin-film transistors, which are the core component of active matrix display technology, and thus printing a high-quality metal oxide functional layer is of great importance. In this feature article, we focused on the current progress in one of the foundations of drop-on-demand printing technology-the ink system. We explained the basic principles of a metal oxide ink system for printed electronics and summarized the applications of several kinds of ink systems in thin film transistor printing. Meanwhile, we also summed up problems that printed thin film transistors are facing as well as the corresponding solutions from the aspect of ink systems.

Morphology Modulation of Direct Inkjet Printing by Incorporating Polymers and Surfactants into a Sol-Gel Ink System.

Many methods have been reported to prevent the nonuniformity of inkjet printing structures. Most of them depend on the balance of the capillary flow in the printing pattern during the evaporation of the solvent. However, as the relation of evaporation and capillary flow can obviously vary among different ink systems, it is difficult for a method to fit most of the situations. Therefore, it would be a promising way to eliminate any capillary flow before solvent evaporation so that morphology of the printing structure will not be affected by the evaporation behavior of the ink system. In this paper, a novel method of direct inkjet printing of a uniform metal oxide structure is reported. We introduce a polymer polyacrylamide and a surfactant FSO into a sol-gel ink system, and the new ink system can gel from the printing pattern edge to center as temperature increases because of the cross-linking of the polymer chains. By that means, transport of solute molecules and solvent molecules is limited. Meanwhile, the surfactant can ensure that the solute in the central liquid phase deposits uniformly by enhancing the Marangoni flow during the gelation process. The ZrO2 film with uniform morphology was fabricated by drying and annealing the gelating film and afforded a leakage current density of 7.48 × 10-7 A cm-2 at 1 MV and a breakdown field of 1.9 MV cm-1 at an annealing temperature of 250 °C.

Capillary force induced air film for self-aligned short channel: pushing the limits of inkjet printing.

Ultrashort channels of electrodes are essential for the construction of advanced functional devices with high-level integration and high operation speed. However, the channel length of fabricated electrodes is limited to 20 µm in inkjet printing. Although several methods have been previously proposed to obtain short channels, they require extra processing steps. In this paper, channel self-aligning phenomenon was observed in directly patterned electrodes on unmodified substrate by inkjet printing, when using an interspace defects growing method. Further exploring the underlying mechanism reveals that the capillary force induced air film prevents droplets coalescence, even on a substrate with no temperature differences. The wetting region, which is generated by the receding droplets impingement, will draw droplets closer together at a larger drop space, thus demanding smaller air pressure for coalescence inhibition and contributing to the self-aligning phenomenon of micro-sized droplets released by inkjet printing. Accordingly, an ultrashort channel of 2.38 µm is obtained with relatively smooth boundaries, when electrodes are printed on a slightly heated substrate, which reduces the air pressure between two neighboring droplets. This work will provide a significant reference for future high resolution applications of inkjet printing technology.

Highly Transparent and Self-Extinguishing Nanofibrillated Cellulose-Monolayer Clay Nanoplatelet Hybrid Films.

A viable solution toward "green" optoelectronics is rooted in our ability to fabricate optoelectronics on transparent nanofibrillated cellulose (NFC) film substrates. However, the flammability of transparent NFC film poses a severe fire hazard in optoelectronic devices. Despite many efforts toward enhancing the fire-retardant features of transparent NFC film, making NFC film fire-retardant while maintaining its high transparency (≥90%) remains an ambitious objective. Herein, we combine NFC with NFC-dispersed monolayer clay nanoplatelets as a fire retardant to prepare highly transparent NFC-monolayer clay nanoplatelet hybrid films with a superb self-extinguishing behavior. Homogeneous and stable monolayer clay nanoplatelet dispersion was initially obtained by using NFC as a green dispersing agent with the assistance of ultrasonication and then used to blend with NFC to prepare highly transparent and self-extinguishing hybrid films by a water evaporation-induced self-assembly process. As the content of monolayer clay nanoplatelets increased from 5 wt % to 50 wt %, the obtained hybrid films presented enhanced self-extinguishing behavior (limiting oxygen index sharply increased from 21% to 96.5%) while retaining a ∼90% transparency at 600 nm. More significantly, the underlying mechanisms for the high transparency and excellent self-extinguishing behavior of these hybrid films with a clay nanoplatelet content of over 30 wt % were unveiled by a series of characterizations such as SEM, XRD, TGA, and limiting oxygen index tester. This work offers an alternative environmentally friendly, self-extinguishing, and highly transparent substrate to next-generation optoelectronics, and is aimed at providing a viable solution to environmental concerns that are caused by ever-increasing electronic waste.

Machine Learning-Guided Performance Evaluation of an All-Liquid Electrochromic Device.

Electrochromic devices, capable of modulating light transmittance under the influence of an electric field, have garnered significant interest in the field of smart windows and car rearview mirrors. However, the development of high-performance electrochromic devices via large-scale explorations under miscellaneous experimental settings remains challenging and is still an urgent problem to be solved. In this study, we employed a two-step machine learning approach, combining machine learning algorithms such as KNN and XGBoost with the reality of electrochromic devices, to construct a comprehensive evaluation system for electrochromic materials. Utilizing our predictive evaluation system, we successfully screened the preparation conditions for the best-performing device, which was experimentally verified to have a high transmittance modulation amplitude (62.6%) and fast response time (5.7 s/7.1 s) at 70 A/m2. To test its stability, experiments over a long cycle time (1000 cycles) are performed. In this study, we develop an innovative framework for assessing the performance of electrochromic material devices. Our approach effectively filters experimental samples based on their distinct properties, substantially minimizing the expenditure of human and material resources in electrochromic research. Our approach to a mathematical machine learning evaluation framework for device performance has effectively propelled and informed research in electrochromic devices.

Flexible and Energy-Efficient Synaptic Transistor with Quasi-Linear Weight Update Protocol by Inkjet Printing of Orientated Polar-Electret/High-k Oxide Composite Dielectric.

Inkjet printing artificial synapse is cost-effective but challenging in emulating synaptic dynamics with a sufficient number of effective weight states under ultralow voltage spiking operation. A synaptic transistor gated by inkjet-printed composite dielectric of polar-electret polyvinylpyrrolidone (PVP) and high-k zirconia oxide (ZrOx) is proposed and thus synthesized to solve this issue. Quasi-linear weight update with a large variation margin is obtained through the coupling effect and the facilitation of dipole orientation, which can be attributed to the orderly arranged molecule chains induced by the carefully designed microfluidic flows. Crucial features of biological synapses including long-term plasticity, spike-timing-dependence-plasticity (STDP), "Learning-Experience" behavior, and ultralow energy consumption (<10 fJ/pulse) are successfully implemented on the device. Simulation results exhibit an excellent image recognition accuracy (97.1%) after 15 training epochs, which is the highest for printed synaptic transistors. Moreover, the device sustained excellent endurance against bending tests with radius down to 8 mm. This work presents a very viable solution for constructing the futuristic flexible and low-cost neural systems.

Research and Progress of Inorganic Infrared Electrochromic Materials and Devices.

BACKGROUND: Electrochromic materials can dynamically change their optical properties (such as transmittance, absorbance, and reflectance under the action of an applied voltage, and their research and application in the visible band have been widely concerned. In recent years, with the continuous development of electrochromic technology, the related research has been gradually extended to the infrared region. OBJECTIVE: This invited review aims to provide an overview of the current status of several inorganic infrared electrochromic materials, to provide some references for future research, and to promote the research and application of electrochromic technology in the infrared region. METHODS: This review summarizes various research results in the field of infrared electrochromic, which includes a detailed literature review and patent search. Starting from the key performance parameters and device structure characteristics of infrared electrochromic devices (ECDs), the research and progress of several types of inorganic infrared electrochromic materials, including metal oxides, plasma nanocrystals, and carbon nanomaterials, are mainly presented, and feasible optimization directions are also discussed. CONCLUSION: We believe that the potential of these materials for civilian and military applications, for example, infrared electrochromic smart windows, infrared stealth/disguise, and thermal control of spacecraft, can be fully exploited by optimizing the materials and their devices to improve their performance.

Effects of Laser Treatment of Terbium-Doped Indium Oxide Thin Films and Transistors.

In this study, a KrF excimer laser with a high-absorption coefficient in metal oxide films and a wavelength of 248 nm was selected for the post-processing of a film and metal oxide thin film transistor (MOTFT). Due to the poor negative bias illumination stress (NBIS) stability of indium gallium zinc oxide thin film transistor (IGZO-TFT) devices, terbium-doped Tb:In2O3 material was selected as the target of this study. The XPS test revealed the presence of both Tb3+ and Tb4+ ions in the Tb:In2O3 film. It was hypothesized that the peak of the laser thermal effect was reduced and the action time was prolonged by the f-f jump of Tb3+ ions and the C-T jump of Tb4+ ions during the laser treatment. Studies related to the treatment of Tb:In2O3 films with different laser energy densities have been carried out. It is shown that as the laser energy density increases, the film density increases, the thickness decreases, the carrier concentration increases, and the optical band gap widens. Terbium has a low electronegativity (1.1 eV) and a high Tb-O dissociation energy (707 kJ/mol), which brings about a large lattice distortion. The Tb:In2O3 films did not show significant crystallization even under laser energy density treatment of up to 250 mJ/cm2. Compared with pure In2O3-TFT, the doping of Tb ions effectively reduces the off-state current (1.16 × 10-11 A vs. 1.66 × 10-12 A), improves the switching current ratio (1.63 × 106 vs. 1.34 × 107) and improves the NBIS stability (ΔVON = -10.4 V vs. 6.4 V) and positive bias illumination stress (PBIS) stability (ΔVON = 8 V vs. 1.6 V).

Effect of Surface Treatment on Performance and Internal Stacking Mode of Electrohydrodynamic Printed Graphene and Its Microsupercapacitor.

Microelectronic devices are developing rapidly in portability, wearability, and implantability. This puts forward an urgent requirement for the delicate deposition process of materials. Electrohydrodynamic printing has attracted academic and industrial attention in preparing ultrahigh-density microelectronic devices as a new noncontact, direct graphic, and low-loss thin film deposition process. In this work, a printed graphene with narrow line width is realized by combining the electrohydrodynamic printing and surface treatment. The line width of printed graphene on the hydrophobic treatment surface reduced from 80 to 28 µm. The resistivity decreased from 0.949 to 0.263 Ω·mm. Unexpectedly, hydrophobic treatment can effectively induce random stacking of electrohydrodynamic printed graphene, which avoids parallel stacking and agglomeration of graphene sheets. The performance of printed graphene is thus effectively improved. After optimization, a graphene planar supercapacitor with a printed line width of 28 µm is successfully obtained. Its capacitance can reach 5.39 mF/cm2 at 50 mV/s, which is twice higher than that of the untreated devices. The device maintains 84.7% capacitance after 5000 cycles. This work provides a reference for preparing microelectronic devices by ultrahigh precision printing and a new direction for optimizing two-dimensional material properties through stacking adjustment.

High-Performance and Stability Electrochromic Devices with a Water Isotopologue.

In this report, an ammonium metatungstate (AMT) and ferrous chloride [Fe(II)Cl2] electrochromic liquid (ECL) was synthesized using a hydrothermal method, with D2O used as the solvent instead of H2O. The results show that the use of D2O can improve the stability and performance of ECLs. The hydrogen evolution process in electrochromic devices (ECDs) filled with ECL becomes more difficult, while the material exchange process becomes easier. The ECD exhibits a color modulation amplitude of 58%@680 nm at 2 V. After 500 cycles, the device's performance remains above 95% at a current density of 1.5 mA/cm2. Hydrogen bonds in D2O solutions are expected to exhibit stronger forces compared to those in regular H2O solutions. Therefore, we hypothesize that enhancing the strength of hydrogen bonds in H2O solutions is an effective approach for improving the performance and stability of electrochromic solutions.

Flexible High-Entropy Poly(vinyl alcohol) Dielectric Films Were Prepared at a Low Temperature and Applied to an Indium Gallium Zinc Oxide Thin-Film Transistor.

In recent years, more and more attention has been paid to flexible thin-film transistors (TFTs). Therefore, we combined HfMgTiYZrOx high-entropy metal oxide and poly(vinyl alcohol) (PVA) organic material to prepare a flexible dielectric layer. We fabricated metal-insulator-metal (MIM) and TFT devices and carried out flexible tests. The test results show that the mixed dielectric layer attains a leakage current of 3.6 × 10-11 A under the bending radius of 5 mm. In the application of the TFT, the device still has good performance after 10 000 bends with a mobility of 3.1 cm2 V-1 s-1, an Ion/Ioff of 1.4 × 107, a threshold voltage of 3.3 V, and a threshold swing of 0.20 V/decade. In addition, the average transmittance of the hybrid dielectric layer in the visible range is 90.8%. Therefore, high-entropy PVA hybrid films have high transparency, low leakage current, and good bending resistance and have broad application prospects in transparent and flexible devices.

Controlled and Sequential Delivery of Stromal Derived Factor-1 α (SDF-1α) and Magnesium Ions from Bifunctional Hydrogel for Bone Regeneration.

Bone healing is a complex process that requires the participation of cells and bioactive factors. Stromal derived factor-1 α (SDF-1α) and magnesium ions (Mg2+) both are significant bioactive factors for cell recruitment and osteogenesis during bone regeneration. Thus, a bifunctional hydrogel containing a sequential delivery system is fabricated to improve osteogenesis. During sequential delivery of the hydrogel, SDF-1α is predominantly released at the early stage of bone mesenchymal stem cells (BMSCs) recruitment, while Mg2+ are constantly delivered at a later stage to improve osteogenic differentiation of recruited cells. In addition, due to the early release of SDF-1α, the hydrogel showed strong BMSCs recruitment and proliferation activity. Mg2+ can not only induce up-regulation of osteogenic gene expression in vitro, but also promote bone tissue and angiogenesis in vivo. Taken together, the injection of xanthan gum-polydopamine crosslinked hydrogel co-loading SDF-1α and Mg2+ (XPMS hydrogel) provides a novel strategy to repair bone defects.

Application of Solution Method to Prepare High Performance Multicomponent Oxide Thin Films.

Capacitors play an increasingly important role in hybrid integrated circuits, while the MIM capacitors with high capacitance density and small thickness can meet the needs of high integration. Generally speaking, the films prepared with a single metal oxide dielectric often achieve a breakthrough in one aspect of performance, but dielectric layers are required to be improved to get better performance in leakage current, capacitance density, and transmittance simultaneously in modern electronic devices. Therefore, we optimized the performance of the dielectric layers by using multiple metal oxides. We combined zirconia, yttria, magnesium oxide, alumina, and hafnium oxide with the solution method to find the best combination of these five metal oxides. The physical properties of the multi-component films were measured by atomic force microscopy (AFM), ultraviolet-visible spectrophotometer, and other instruments. The results show that the films prepared by multi-component metal oxides have good transmittance and low roughness. The thicknesses of all films in our experiment are less than 100 nm. Then, metal-insulator-metal (MIM) devices were fabricated. In addition, we characterized the electrical properties of MIM devices. We find that multi-component oxide films can achieve good performances in several aspects. The aluminum-magnesium-yttrium-zirconium-oxide (AMYZOx) group of 0.6 M has the lowest leakage current density, which is 5.03 × 10-8 A/cm2 @ 1.0 MV/cm. The hafnium-magnesium-yttrium-zirconium-oxide (HMYZOx) group of 0.8 M has a maximum capacitance density of 208 nF/cm2. The films with a small thickness and a high capacitance density are very conducive to high integration. Therefore, we believe that multi-component films have potential in the process of dielectric layers and great application prospects in highly integrated electronic devices.

Solution-Processed Silicon Doped Tin Oxide Thin Films and Thin-Film Transistors Based on Tetraethyl Orthosilicate.

Recently, tin oxide (SnO2) has been the preferred thin film material for semiconductor devices such as thin-film transistors (TFTs) due to its low cost, non-toxicity, and superior electrical performance. However, the high oxygen vacancy (VO) concentration leads to poor performance of SnO2 thin films and devices. In this paper, with tetraethyl orthosilicate (TEOS) as the Si source, which can decompose to release heat and supply energy when annealing, Si doped SnO2 (STO) films and inverted staggered STO TFTs were successfully fabricated by a solution method. An XPS analysis showed that Si doping can effectively inhibit the formation of VO, thus reducing the carrier concentration and improving the quality of SnO2 films. In addition, the heat released from TEOS can modestly lower the preparation temperature of STO films. By optimizing the annealing temperature and Si doping content, 350 °C annealed STO TFTs with 5 at.% Si exhibited the best device performance: Ioff was as low as 10-10 A, Ion/Ioff reached a magnitude of 104, and Von was 1.51 V. Utilizing TEOS as an Si source has a certain reference significance for solution-processed metal oxide thin films in the future.

A Strategy toward Realizing Narrow Line with High Electrical Conductivity by Electrohydrodynamic Printing.

Over the past few decades, electrohydrodynamic (EHD) printing has proved to be an environmentally friendly, cost-effective and powerful tool in manufacturing electronic devices with a wire width of less than 50 µm. In particular, EHD printing is highly valued for the printing of ultrafine wire-width silver electrodes, which is important in manufacturing large-area, high-resolution micron-scale or even nanoscale structures. In this paper, we compare two methods of surface modification of glass substrate: UV treatment and oxygen plasma treatment. We found that oxygen plasma was better than UV treatment in terms of wettability and uniformity. Secondly, we optimized the annealing temperature parameter, and found that the conductivity of the electrode was the highest at 200 °C due to the smoothing silver electrode and the oxidation-free internal microstructure. Thirdly, we used EHD printing to fabricate silver electrodes on the glass substrate. Due to the decrease of conductivity as a result of the skin effect and the decrease of silver content, we found that driving voltage dropped, line width decreased, and the conductivity of silver line decreased. After the optimization of the EHD printing process, Ag electrode line width and conductivity reached 19.42 ± 0.24 µm and 6.01 × 106 S/m, demonstrating the potential of electro-hydraulic printing in the manufacturing of flexible, wearable, high-density, low-power-consumption electronics.

Investigation of an Electrochromic Device Based on Ammonium Metatungstate-Iron (II) Chloride Electrochromic Liquid.

Even though electrochromism has been around for more than 50 years, it still has several issues. Multi-layered films, high manufacturing costs, and a short lifetime are present in existing electrochromic devices. We demonstrate a unique high-performance device with a basic structure and no solid electrochromic sheets in this work. In this device, the electrolyte layer is also avoided. The device uses an electrochromic solution prepared from a mixture of ammonium metatungstate and iron (II) chloride solution as a functional layer with reversible redox properties. The tungstate ions on the electrode surface are reduced when the device is colored, and the Fe2+ on the electrode surface is oxidized on another electrode surface. The generated Fe3+ in the mixed functional layer oxidizes the previously reduced tungstate ions as the device fades. We determined the ΔT (transmittance modulation) and response time among ammonium metatungstate ratios, iron (II) chloride ratios, and driven current density using DOE (design of experiment) trials. Using 0.175 mol/L ammonium metatungstate and 0.30 mol/L iron (II) chloride, a device with outstanding ΔT (more than 57% at 700 nm), a short response time (less than 10 s), and high coloring efficiency (160.04 cm2/C at 700 nm) is demonstrated.

Research Progresses in Microstructure Designs of Flexible Pressure Sensors.

Flexible electronic technology is one of the research hotspots, and numerous wearable devices have been widely used in our daily life. As an important part of wearable devices, flexible sensors can effectively detect various stimuli related to specific environments or biological species, having a very bright development prospect. Therefore, there has been lots of studies devoted to developing high-performance flexible pressure sensors. In addition to developing a variety of materials with excellent performances, the microstructure designs of materials can also effectively improve the performances of sensors, which has brought new ideas to scientists and attracted their attention increasingly. This paper will summarize the flexible pressure sensors based on material microstructure designs in recent years. The paper will mainly discuss the processing methods and characteristics of various sensors with different microstructures, and compare the advantages, disadvantages, and application scenarios of them. At the same time, the main application fields of flexible pressure sensors based on microstructure designs will be listed, and their future development and challenges will be discussed.