Ultrathin Al2O3film modification on waterborne epoxy coatings by atomic layer deposition for augmenting the corrosion resistance

The polar channels formed by the curing of waterborne anticorrosive coatings compromise their water resistance, leading to coating degradation and metal corrosion. To enhance the anticorrosive performance of waterborne coatings, this study proposed a novel method of depositing ultrathin Al2O3films on the surface of waterborne epoxy coatings by atomic layer deposition, a technique that can modify the surface properties of polymer materials by depositing functional films. The Al2O3-modified coatings exhibited improved sealing and barrier properties by closing the polar channels and surface defects and cracks. The surface structure and morphology of the modified coatings were characterized by x-ray photoelectron spectroscopy and scanning electron microscopy. The hydrophilicity and corrosion resistance of the modified coatings were evaluated by water contact angle measurement, Tafel polarization curve, and electrochemical impedance spectroscopy. The results indicated that the water contact angle of the Al2O3-modified coating increased by 48° compared to the unmodified coating, and the protection efficiency of the modified coating reached 99.81%. The Al2O3-modified coating demonstrated high anticorrosive efficiency and potential applications for metal anticorrosion in harsh marine environments.

Importance of Structural Relaxation on the Electrical Characteristics and Bias Stability of Solution-Processed ZnSnO Thin-Film Transistors

Effect of structural relaxation (SR) on the electrical characteristics and bias stability of solution-processed zinc-tin oxide (ZTO) thin-film transistors (TFTs) were systematically investigated by controlling the annealing time of the ZTO semiconductor films. Note that SR was found to increase with increased annealing time. Due to the increased SR, the ratio of oxygen vacancies (V_O) increased from 21.5% to 38.2%. According to increased V_O, the mobility in the saturation region was exhibited by a sixfold increase from 0.38 to 2.41 cm² V^-1 s^-1. In addition, we found that the threshold voltage negatively shifted from 3.08 to -0.95 V. Regarding the issue of bias stability, according to increased SR, positive-bias stress of the ZTO TFTs was enhanced, compared with reverse features of negative-bias stress. Our understanding is expected to provide a basic way to improve the electrical characteristics and bias stability of rare-metal-free oxide semiconductor TFTs, which have not been sufficiently studied.

Synaptic transistors with aluminum oxide dielectrics enabling full audio frequency range signal processing

The rapid evolution of the neuromorphic computing stimulates the search for novel brain-inspired electronic devices. Synaptic transistors are three-terminal devices that can mimic the chemical synapses while consuming low power, whereby an insulating dielectric layer physically separates output and input signals from each other. Appropriate choice of the dielectric is crucial in achieving a wide range of operation frequencies in these devices. Here we report synaptic transistors with printed aluminum oxide dielectrics, improving the operation frequency of solution-processed synaptic transistors by almost two orders of magnitude to 50 kHz. Fabricated devices, yielding synaptic response for all audio frequencies (20 Hz to 20 kHz), are employed in an acoustic response system to show the potential for future research in neuro-acoustic signal processing with printed oxide electronics.

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.

Solution-Processed, Electrolyte-Gated In2O3 Flexible Synaptic Transistors for Brain-Inspired Neuromorphic Applications

Emulating the essential synaptic behaviors using single synaptic transistor has attracted extensive attention for building the brain-inspired neuromorphic systems. However, few reports on synaptic transistors fabricated by solution processes have been reported. In this article, the indium oxide synaptic transistors based on polyimide substrates were fabricated by a nontoxic water-inducement method at a low temperature, and lithium perchlorate (LiClO₄) was dissolved in polyethylene oxide as the gate electrolyte. For water-inducement process, comparable electrical properties of the synaptic transistors can be achieved by prolonging the annealing time rather than high-temperature annealing with a relatively short time. The effect of the annealing time on the electrical performance of the electrolyte-gated transistors annealed at various temperatures was investigated. It is found that the electrolyte-gated-synaptic transistor on polyimide substrate annealed at 200 °C exhibits high electrical performance and good mechanical stability. Due to the ion migration relaxation dynamics in the polymer electrolyte, various important synaptic behaviors such as the excitatory postsynaptic current, paired-pulse facilitation, high-pass filtering characteristics, and long-term memory performance were successfully mimicked. The electrolyte-gated synaptic transistors based on solution-processed In₂O₃ exhibit great potential in neuromorphological applications.

Synthesis, oxide formation, properties and thin film transistor properties of yttrium and aluminium oxide thin films employing a molecular-based precursor route

Combustion synthesis of dielectric yttrium oxide and aluminium oxide thin films is possible by introducing a molecular single-source precursor approach employing a newly designed nitro functionalized malonato complex of yttrium (Y-DEM-NO21) as well as defined urea nitrate coordination compounds of yttrium (Y-UN 2) and aluminium (Al-UN 3). All new precursor compounds were extensively characterized by spectroscopic techniques (NMR/IR) as well as by single-crystal structure analysis for both urea nitrate coordination compounds. The thermal decomposition of the precursors 1-3 was studied by means of differential scanning calorimetry (DSC) and thermogravimetry coupled with mass spectrometry and infrared spectroscopy (TG-MS/IR). As a result, a controlled thermal conversion of the precursors into dielectric thin films could be achieved. These oxidic thin films integrated within capacitor devices are exhibiting excellent dielectric behaviour in the temperature range between 250 and 350 °C, with areal capacity values up to 250 nF cm-2, leakage current densities below 1.0 × 10-9 A cm-2 (at 1 MV cm-1) and breakdown voltages above 2 MV cm-1. Thereby the increase in performance at higher temperatures can be attributed to the gradual conversion of the intermediate hydroxy species into the respective metal oxide which is confirmed by X-ray photoelectron spectroscopy (XPS). Finally, a solution-processed Y x O y based TFT was fabricated employing the precursor Y-DEM-NO21. The device exhibits decent TFT characteristics with a saturation mobility (μ sat) of 2.1 cm2 V-1 s-1, a threshold voltage (V th) of 6.9 V and an on/off current ratio (I on/off) of 7.6 × 105.

Polymer-Assisted Deposition of Gallium Oxide for Thin-Film Transistor Applications

We report the fabrication of gallium oxide (GaO_x) thin films by a novel polymer-assisted deposition (PAD) method. The influence and mechanism of postannealing temperature (200-800 °C) on the formation and properties of GaO_x thin films are investigated by complementary characterization analyses. The results indicate that solution-deposited GaO_x experiences the elimination of organic residuals as well as the transformation of amorphous GaO_x to crystalline GaO_x with the increase in annealing temperature. High-quality GaO_x could be achieved with a smooth surface, wide band gap, and decent dielectric performance. Moreover, the solution-processed In₂O₃ thin-film transistors based on optimized GaO_x dielectrics demonstrate outstanding electrical performance, including a low operating voltage of 5 V, a mobility of 3.09 cm² V^-1 s^-1, an on/off current ratio of 1.8 × 10⁵, and a subthreshold swing of 0.18 V dec^-1. Our study suggests that GaO_x achieved by PAD shows great potential for further low-cost and high-performance optoelectronic applications.

Inkjet-Printed Oxide Thin-Film Transistors Based on Nanopore-Free Aqueous-Processed Dielectric for Active-Matrix Quantum-Dot Light-Emitting Diode Displays

Inkjet-printed thin-film transistors (TFTs) for active-matrix light-emitting diode display are drawing much attention for the advantages of low material waste and simple fabrication processes without vacuum deposition and photolithography steps. Herein, for the first time, solution-processed quantum-dot light-emitting diode (QLED) array displays driven with the inkjet-printed oxide TFT backplane were realized and demonstrated using a general "solvent printing" method. To suppress nanopore formation in the thick oxide films, carbon-free aqueous inks were employed for gate dielectrics. No nanopore was found in the whole 120 nm-thick gate dielectrics. However, compared to the organic inks, the aqueous inks have very low viscosity, resulting in uncontrollable ink spreading especially in transline printing. The ink easily shrinks on the low-surface-energy area and spreads on the high-surface-energy area, leading to serious uniformity problems (the upper lines even break at the top of underlying lines). To solve the problem, a "solvent printing" method was employed to form coffee-line surface-energy patterns, which were uniform without shape distortion. The surface-energy patterns can restrain the ink spreading and tune the morphology of the printed films. As a result, multilayer TFT arrays with ideal shapes were achieved. The mobilities of the printed top-gate TFTs in the backplane array were 3.13 ± 0.87 cm² V^-1 s^-1 for switching TFTs and 2.22 ± 0.38 cm² V^-1 s^-1 for driving TFTs. Finally, an active-matrix red QLED character display based on the printed oxide TFT backplane and solution-processed QLEDs was demonstrated. The "solvent printing" method opens a general route for inkjet-printed multilayer electronic devices.

Optimization of the Anodization Processing for Aluminum Oxide Gate Dielectrics in ZnO Thin Film Transistors by Multivariate Analysis

The present study reports a two-level multivariate analysis to optimize the production of anodized aluminum oxide (Al₂O₃) dielectric films for zinc oxide thin-film transistors (TFTs). Fourteen performance parameters were measured and analysis of variance (ANOVA) of the combined responses has been applied to identify how the Al₂O₃ dielectric fabrication process influences the electrical properties of the TFTs. Using this approach, the levels for the manufacturing factors to achieve optimal overall device performance have been identified and ranked. The cross-checked analysis of the TFT performance parameters demonstrated that the appropriate control of the anodization process can have a higher impact on TFT performance than the use of traditional methods of surface treatment of the dielectric layer. Flexible electronics applications are expected to grow substantially over the next 10 years. Given the complexity and challenges of new flexible electronics components, this "multivariate" approach could be adopted more widely by the industry to improve the reliability and performance of such devices.

Molecular dynamics simulation on the reaction of nano-aluminum with water: size and passivation effects

The reaction of aluminum and water is widely used in the field of propulsion and hydrogen production, but its reaction characteristics at the nanometer scale have not been fully studied. In this paper, the effect of particle size and surface passivation of aluminum particle on the reaction mechanism was studied by using reactive molecular dynamics (RMD) simulation. The reduction of aluminum particle size can accelerate the reaction rate in the medium term (20–80 ps) due to the increase of activity, but it also produces an agglomeration effect as the temperature increases. The presence of surface passivation reduces the proportion of active aluminum and the yield of hydrogen decreases by 30% and 33%, respectively, as the particle size decreases from 2.5 nm to 1.6 nm. The addition of AlH₃ can overcome these drawbacks when some aluminum powders are replaced by AlH₃. The hydrogen yield is increased by the reaction 2AlH₃ + 3H₂O → Al₂O₃ + 6H₂. In the reaction of surface passivated Al (1.6 nm in diameter) and H₂O, when the proportion of AlH₃ reaches 25%, the energy release and hydrogen yield increase from 59.47 kJ mol⁻¹ and 0.0042 mol g⁻¹ to 142.56 kJ mol⁻¹ and 0.0076 mol g⁻¹, respectively. This performance even approximates the reaction of pure aluminum with water: 180.67 kJ mol⁻¹ and 0.0087 mol g⁻¹. In addition, the surface passivation affects the reaction mechanism. Before the passivation layer melts, the reaction 4Al + Al₂O₃ → 3Al₂O occurs inside the nanoparticles.

The temperature distribution, number of Al–O bonds and hydrogen yield evolution with time.

Potential solution-induced HfAlO dielectrics and their applications in low-voltage-operating transistors and high-gain inverters

Recently, much attention has been paid to the investigation of solution-driven oxides for application in thin film transistors (TFTs). In current study, a fully solution-based method, using 2-methoxyethanol as solvent, has been adopted to prepare InZnO thin films and HfAlO _x gate dielectrics. Amorphous HfAlO _x thin films annealed at 600 °C have shown a high transparency (>85%), low leakage current density (6.9 × 10^-9 A cm^-2 at 2 MV cm^-1), and smooth surface. To verify the potential applications of HfAlO _x gate dielectrics in oxide-based TFTs, fully solution-induced InZnO/HfAlO _x TFTs have been integrated. Excellent electrical performance for InZnO/HfAlO _x TFTs annealed at 450 °C has been observed, including a low operating voltage of 3 V, a saturated mobility of 5.17 cm² V^-1 s^-1, a high I _on/I _off of ∼10⁶, a small subthreshold swing of 87 mV per decade, and a threshold voltage shift of 0.52 V under positive bias stress (PBS) for 7200 s, respectively. In addition, time dependent threshold voltage shift under PBS could be described by a stretched-exponential model, which can be due to charge trapping in the semiconductor/dielectric interface. Finally, to explore the possible application in logic operation, a resistor-loaded inverter based on InZnO/HfAlO _x TFTs has been built and excellent swing characteristic and well dynamic behavior have been obtained. Therefore, it can be concluded that fully solution-driven InZnO/HfAlO _x TFTs have demonstrated potential application in nontoxic, eco-friendly and low-power consumption oxide-based flexible electronics.

Electrospun p-Type Nickel Oxide Semiconducting Nanowires for Low-Voltage Field-Effect Transistors

One-dimensional metal-oxide nanowires are regarded as important building blocks in nanoscale electronics, because of their unique mechanical and electrical properties. In this work, p-type nickel oxide nanowires (NiO NWs) were fabricated by combining sol-gel and electrospinning processes. The poly(vinylpyrrolidone) (PVP) with a molecular weight of 1 300 000 was used as the polymer matrix to increase the viscosity of a NiO precursor solution. The formation and properties of the as-spun NiO/PVP composite NWs before/after calcination treatment were investigated using various techniques. Because of the enhanced adhesion properties between ultraviolet (UV)-treated NiO NWs and the substrate, the field-effect transistors (FETs) based on NiO NWs were found to exhibit satisfying p-channel behaviors. For the fabrication of aligned NiO NW arrays, two parallel conducting Si strips were grounded as NW collector. The integrated FETs based on aligned NiO NWs were demonstrated to exhibit superior electrical performance, compared to the disordered counterparts with the comparable NW coverage. By employing high- k aluminum oxide (Al₂O₃) as a dielectric layer, instead of conventional SiO₂, the devices with an aligned NiO NW array exhibit a high hole mobility of 2.8 cm²/(V s) with a low operating voltage of 5 V, fast switching speed, and successful modulation of light emission over external light-emitting diodes. To the best of our knowledge, this is the first work demonstrating the low-voltage transistors based on p-type oxide NWs, which represents a great step toward the development of sensors and CMOS logic circuits.

Solution Processed Metal Oxide High-κ Dielectrics for Emerging Transistors and Circuits

The electronic functionalities of metal oxides comprise conductors, semiconductors, and insulators. Metal oxides have attracted great interest for construction of large-area electronics, particularly thin-film transistors (TFTs), for their high optical transparency, excellent chemical and thermal stability, and mechanical tolerance. High-permittivity (κ) oxide dielectrics are a key component for achieving low-voltage and high-performance TFTs. With the expanding integration of complementary metal oxide semiconductor transistors, the replacement of SiO2 with high-κ oxide dielectrics has become urgently required, because their provided thicker layers suppress quantum mechanical tunneling. Toward low-cost devices, tremendous efforts have been devoted to vacuum-free, solution processable fabrication, such as spin coating, spray pyrolysis, and printing techniques. This review focuses on recent progress in solution processed high-κ oxide dielectrics and their applications to emerging TFTs. First, the history, basics, theories, and leakage current mechanisms of high-κ oxide dielectrics are presented, and the underlying mechanism for mobility enhancement over conventional SiO2 is outlined. Recent achievements of solution-processed high-κ oxide materials and their applications in TFTs are summarized and traditional coating methods and emerging printing techniques are introduced. Finally, low temperature approaches, e.g., ecofriendly water-induced, self-combustion reaction, and energy-assisted post treatments, for the realization of flexible electronics and circuits are discussed.

Strong Influence of Humidity on Low-Temperature Thin-Film Fabrication via Metal Aqua Complex for High Performance Oxide Semiconductor Thin-Film Transistors

Oxide semiconductors thin film transistors (OS TFTs) with good transparency and electrical performance have great potential for future display technology. In particular, solution-processed OS TFTs have been attracted much attention due to many advantages such as continuous, large scale, and low cost processability. Recently, OS TFTs fabricated with a metal aqua complex have been focused because they have low temperature processability for deposition on flexible substrate as well as high field-effect mobility for application of advanced display. However, despite some remarkable results, important factors to optimize their electrical performance with reproducibility and uniformity have not yet been achieved. Here, we newly introduce the strong effects of humidity to enhance the electrical performance of OS TFTs fabricated with the metal aqua complex. Through humidity control during the spin-coating process and annealing process, we successfully demonstrate solution-processed InO_x/SiO₂ TFTs with a good electrical uniformity of ∼5% standard deviation, showing high average field-effect mobility of 2.76 cm²V^-1s^-1 and 15.28 cm²V^-1s^-1 fabricated at 200 and 250 °C, respectively. Also, on the basis of the systematic analyses, we demonstrate the mechanism for the change in electrical properties of InO_x TFTs depending on the humidity control. Finally, on the basis of the mechanism, we extended the humidity control to the fabrication of the AlO_x insulator. Subsequently, we successfully achieved humidity-controlled InO_x/AlO_x TFTs fabricated at 200 °C showing high average field-effect mobility of 9.5 cm²V^-1s^-1.

Direct transfer of graphene and application in low-voltage hybrid transistors

Scotch tape assisted direct transfer of graphene is presented. Transferred graphene can act as a carrier transport layer in In₂O₃/graphene/ZrO₂transistor.

Tunable high-κ ZrxAl1−xOy thin film dielectrics from all-inorganic aqueous precursor solutions

An all-inorganic, aqueous solution route enables facile control of composition and optimization of zirconium aluminum oxide thin film dielectric properties.