Roll-to-roll Research Articles

High-quality AlN epilayers prepared by atomic layer deposition and large-area rapid electron beam annealing

Low-temperature atomic layer deposition and high-temperature electron beam annealing (EBA) are used to achieve high-quality epitaxial AlN layers. Efficient energy transfer from the single exposure for only 1 min of electron irradiation with a large area contributes to substantial improvement in the film density and crystal quality of AlN thin films, as demonstrated by the X-ray reflectivity and the θ-2θ/ω-scan X-ray diffraction. High-resolution transmission electron microscopy indicates well-arranged lattice fringes in the epitaxial AlN layer on a sapphire substrate. A low surface roughness of the AlN epilayer, as revealed by the atomic force microscopy, suggests that the damage induced by the EBA treatment is insignificant. The outcomes indicate that the large-area rapid EBA is a low-damage and efficient technique for the recrystallization of thin films prepared at low temperatures.

Large-Area Electronics-Enabled High-Resolution Digital Microfluidics for Parallel Single-Cell Manipulation.

Large-area electronics as switching elements are an ideal option for electrode-array-based digital microfluidics. With support of highly scalable thin-film semiconductor technology, high-resolution digital droplets (diameter around 100 μm) containing single-cell samples can be manipulated freely on a two-dimensional plane with programmable addressing logic. In addition, single-cell generation and manipulation as foundations for single-cell research demand ease of operation, multifunctionality, and accurate tools. In this work, we reported an active-matrix digital microfluidic platform for single-cell generation and manipulation. The active device contained 26,368 electrodes that could be independently addressed to perform parallel and simultaneous droplet generation and achieved single-cell manipulation. We demonstrate a high-resolution digital droplet generation with a droplet volume limit of 500 pL and show the continuous and stable movement of droplet-contained cells for over 1 h. Furthermore, the success rate of single droplet formation was higher than 98%, generating tens of single cells within 10 s. In addition, a pristine single-cell generation rate of 29% was achieved without further selection procedures, and the droplets containing single cells could then be tested for on-chip cell culturing. After 20 h of culturing, about 12.5% of the single cells showed cell proliferation.

The impact of multi-layered dielectrics on the electrical performance of ZnO thin-film transistors

The electrical performance of ZnO thin film transistors (TFTs) fabricated on three different dielectric layers is investigated using an inverted staggered bottom gate thin film transistor structure. This work demonstrated the potential of integrating high-k dielectrics in ZnO TFTs in a dielectric multi-layered stack using SiO2 as the support layer for all the hero-dielectrics layers. In order to achieve this, ZnO thin film semiconducting layers were deposited at room temperature by radio frequency (RF) sputtering method and with no post deposition heat treatment, making them suitable candidates for low cost large area electronics on low temperature substrates (such as plastics). The dielectric films investigated were aluminium nitride (AlN), silicon nitride (SiN) and silicon dioxide (SiO2). The effective mobility of SiN devices was about half that observed in AlN devices. However, the dielectric layers exhibited hysteresis of approximately 0 V, 2 V and 7 V for the SiO2, AlN and SiN respectively. In addition, SiO2 TFTs have lowest threshold voltage (VT) and turn-on voltage (Von). The capacitance-voltage measurement for these device show that the flatband and threshold voltage of SiN and AlN MOS capacitors shifted towards more negative voltages instead when compared with the single layer SiO2 devices.

Multifunctional soft stretchable strain sensor for complementary optical and electrical sensing of fatigue cracks

Fatigue-induced cracking in steel components and other brittle materials of civil structures is one of the primary mechanisms of degrading structural integrity and can lead to sudden failures. However, these cracks are often difficult to detect during visual inspections, and off-the-shelf sensing technologies can generally only be used to monitor already identified cracks because of their spatial localization. A solution is to leverage advances in large area electronics to cover large surfaces with skin-type sensors. Here, the authors propose an elastic and stretchable multifunctional skin sensor that combines optical and capacitive sensing properties. The multifunctional sensor consists of a soft stretchable structural color film sandwiched between transparent carbon nanotube electrodes to form a parallel plate capacitor. The resulting device exhibits a reversible and repeatable structural color change from light blue to deep blue with an angle-independent property, as well as a measurable change in capacitance, under external mechanical strain. The optical function is passive and engineered to visually assist in localizing fatigue cracks, and the electrical function is added to send timely warnings to infrastructure operators. The performance of the device is characterized in a free-standing configuration and further extended to a fatigue crack monitoring application. A correlation coefficient-based image processing method is developed to quantify the strain measured by the optical color response. Results show that the sensor performs well in detecting and quantifying fatigue cracks using both the color and capacitive signals. In particular, the color signal can be measured with inexpensive cameras, and the electrical signal yields good linearity, resolution, and accuracy. Tests conducted on two steel specimens demonstrate a minimum detectable crack length of 0.84 mm.

A stretchable nanoscale dielectric for large-area wearable electronics

A stretchable nanoscale dielectric for large-area wearable electronics

High-Performance 1-V IGZO Thin-Film Transistors Gated With Aqueous and Organic Electrolyte-Anodized Al x O y

In this work, ultrathin AlxOy films used as gate dielectrics in thin-film transistors (TFTs) are prepared in aqueous and organic electrolytes using an anodization process. A series of anodization voltages are used to investigate the effects of anodization electrolyte on the surface morphologies and electrical properties of AlxOy films. By using such anodized AlxOy films as gate dielectrics, 1-V indium–gallium–zinc–oxide (IGZO) TFTs are fabricated. The electrical characteristics of the IGZO TFTs with AlxOy films prepared in organic electrolyte are enhanced in comparison with those of the IGZO TFTs with AlxOy films prepared in aqueous electrolyte. The enhancement may be due to more carbon species introduced to the anodized dielectric films. This work offers a method to further improve the properties of ultrathin anodized dielectrics and shows the potential of using anodization in the future for large-area low-power electronics.

Optimizing Photonic Annealing Technique for High-k Dielectric of Full-Solution-Processed Oxide Thin Film Transistor

In this article, it is demonstrated that the photonic annealing process of ultraviolet (UV) irradiation or rapid thermal annealing (RTA)-assisted LA technique can effectively enhance the bias and illumination stability of full-solution-processed oxide thin film transistor (TFT). Although both post-annealing treatments have comparable effects, UV irradiation has relatively less heat loss and time consumption of only 3 min, compared to the RTA process that heats at a temperature of 400 °C and holds 10 min. Depending on the laser annealing (LA)/UV technique, the amorphous hafnium-aluminum oxide (HAO) dielectric thin film exhibits a smooth surface with an rms value of 0.293 nm, a high optical bandgap of 6.19 eV, and good dielectric performance with high dielectric constants of 12.9, low leakage current densities, and high breakdown field of about 4 MV/cm. Moreover, full-solution-processed indium-tin-oxide (ITO)–HAO–tungsten-zinc-tin-oxide (WZTO) TFT shows excellent overall properties with the mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> ) of 10.65 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}}\cdot \text{V}^{-{1}}\cdot \text{s}^{-{1}}$ </tex-math></inline-formula> , subthreshold swing (SS) of 198 mV/dec. And the device has good bias and illumination stability, especially the threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T}$ </tex-math></inline-formula> ) shifts are all less than 3 V under positive bias illumination stress (PBIS) and negative bias illumination stress (NBIS) testing for 10000 s. These indicate the potential for the photonic annealing process of the UV-assisted LA technique on improving the stability of the full-solution-processed TFTs, which is attributed to high-throughput fabrication for large-area, transparent, and flexible electronics.

Ferroelectric Wide-Bandgap Metal Halide Perovskite Field-Effect Transistors: Toward Transparent Electronics.

Transparent field-effect transistors (FETs) are attacking intensive interest for constructing fancy "invisible" electronic products. Presently, the main technology for realizing transparent FETs is based on metal oxide semiconductors, which have wide-bandgap but generally demand sputtering technique or high-temperature (>350°C) solution process for fabrication. Herein, a general device fabrication strategy for metal halide perovskite (MHP) FETs is shown, by which transparent perovskite FETs are successfully obtained using low-temperature (<150°C) solution process. This strategy involves the employment of ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) as the dielectric, which conquers the challenging issue of gate-electric-field screening effect in MHP FETs. Additionally, an ultra-thin SnO2 is inserted between the source/drain electrodes and MHPs to facilitate electron injection. Consequently, n-type semi-transparent MAPbBr3 FETs and fully transparent MAPbCl3 FETs which can operate well at room temperature with mobility over 10-3 cm2 V-1 s-1 and on/off ratio >103 are achieved for the first time. The low-temperature solution processability of these FETs makes them particularly attractive for applications in low-cost, large-area transparent electronics.

Publisher Correction: Wirelessly powered large-area electronics for the Internet of Things

Publisher Correction: Wirelessly powered large-area electronics for the Internet of Things

Fully Sprayed Metal Oxide Transistors Utilizing Ti3C2Tx MXene Contacts

Printable large-area electronics continue to attract increasing interest from the scientific and industrial communities, owing to their potential for cost-efficient manufacturing. However, the exerted efforts primarily focus on processing semiconductors and dielectrics, with relatively limited attention toward printable electrode materials. In this respect, the family of two-dimensional (2D) transition metal carbides/nitrides, so-called MXenes, have emerged as promising electrode materials owing to their metal-like conductivity and solution processability. Despite their advantageous characteristics, however, to date, the application of MXene electrodes in the area of printed electronics has been marginally explored. Herein, we develop all-solution-processable In2O3/ZnO heterojunction metal oxide thin-film transistors (TFTs) utilizing Ti3C2Tx MXene as the gate and the electron-injecting contacts, entirely spray-coated under ambient conditions. We show that the manufacturing of these fully spray-coated devices can be scaled-up to 4 in. substrates without compromising their operating characteristics. The fabricated TFTs exhibit electron mobility of 3 cm2 V–1 s–1 with an on/off ratio of >104. Our findings demonstrate the possibility of replacing conventional metal contacts with spray-coated MXene electrodes for application in large-area electronics.

Printing via Laser-Induced Forward Transfer and the Future of Digital Manufacturing.

In the last decades, digital manufacturing has constituted the headline of what is starting to be known as the 'fourth industrial revolution', where the fabrication processes comprise a hybrid of technologies that blur the lines between fundamental sciences, engineering, and even medicine as never seen before. One of the reasons why this mixture is inevitable has to do with the fact that we live in an era that incorporates technology in every single aspect of our daily lives. In the industry, this has translated into fabrication versatility, as follows: design changes on a final product are just one click away, fabrication chains have evolved towards continuous roll-to roll processes, and, most importantly, the overall costs and fabrication speeds are matching and overcoming most of the traditional fabrication methods. Laser-induced forward transfer (LIFT) stands out as a versatile set of fabrication techniques, being the closest approach to an all-in-one additive manufacturing method compatible with virtually any material. In this technique, laser radiation is used to propel the material of interest and deposit it at user-defined locations with high spatial resolution. By selecting the proper laser parameters and considering the interaction of the laser light with the material, it is possible to transfer this technique from robust inorganic materials to fragile biological samples. In this work, we first present a brief introduction on the current developments of the LIFT technique by surveying recent scientific review publications. Then, we provide a general research overview by making an account of the publication and citation numbers of scientific papers on the LIFT technique considering the last three decades. At the same time, we highlight the geographical distribution and main research institutions that contribute to this scientific output. Finally, we present the patent status and commercial forecasts to outline future trends for LIFT in different scientific fields.

Mo-rich layer formation on maraging steel and surface modification by large-area electron beam irradiation

Maraging steels have been typically applied to precise metal mold and products in aerospace industry, since they have excellent properties such as high strength and toughness. However, the maraging steels are inferior to other steels in some surface functions such as corrosion resistance. Hence, it is necessary to improve surface functions of maraging steel. On the other hand, large-area electron beam (EB) of 60 mm in diameter can instantly melt metal surface. Our previous study clarified that the surface roughness of alloy tool steels such as SKD11 in JIS specification could be reduced efficiently by the EB irradiation. Furthermore, the surface characteristics were also improved by formation of thin re-solidified layer with a fine microstructure. In this study, formation of Mo-rich layer in re-solidified layer on maraging steel surface by large-area EB irradiation was investigated. Mechanism for formation of Mo-rich layer was discussed by unsteady heat conduction analysis. In addition, surface finishing and improvement of surface characteristics of maraging steels by the EB irradiation were also examined. The experimental results show that surface roughness decreases to approximately 1.0µm R z in a few minutes under low energy densities conditions, and Mo-rich layer with thickness of a few micrometers is self-formed in re-solidified layer of EB irradiated surface. Moreover, water repellency, corrosion resistance and wear performance are improved by the formation of Mo-rich layer in re-solidified layer. Therefore, maraging steel surface can be finished and modified simultaneously by large-area EB irradiation method.

Wirelessly powered large-area electronics for the Internet of Things

Powering the increasing number of sensor nodes used in the Internet of Things creates a technological challenge. The economic and sustainability issues of battery-powered devices mean that wirelessly powered operation—combined with environmentally friendly circuit technologies—will be needed. Large-area electronics—which can be based on organic semiconductors, amorphous metal oxide semiconductors, semiconducting carbon nanotubes and two-dimensional semiconductors—could provide a solution. Here we examine the potential of large-area electronics technology in the development of sustainable, wirelessly powered Internet of Things sensor nodes. We provide a system-level analysis of wirelessly powered sensor nodes, identifying the constraints faced by such devices and highlighting promising architectures and design approaches. We then explore the use of large-area electronics technology in wirelessly powered Internet of Things sensor nodes, with a focus on low-power transistor circuits for digital processing and signal amplification, as well as high-speed diodes and printed antennas for data communication and radiofrequency energy harvesting.

Why Micro Printing Is the Future of Large-Area Electronics

Why Micro Printing Is the Future of Large-Area Electronics

In situ transformation of TiO2 hierarchical nanostructures toward efficient photoelectrochemical water splitting

TiO2 hierarchical nanomaterials have been intensively investigated as a very promising photoanode in photoelectrochemical water splitting due to its combined effects of large surface area and fast electron transfer. However, the TiO2 hierarchical nanostructures prepared by most prevailing synthesis methods currently are at distinct disadvantages such as complicated process, poor controllability, poor interfacial contact, excessive impurities and so on. Here we report a facile route to construct a well-defined TiO2 hierarchical nanostructure via in-situ transformation of TiO2 nanoparticles with highly exposed {001} facets in the tube wall of the pristine TiO2 nanotube arrays. The resulted TiO2 hierarchical nanostructures exhibit enhanced light harvesting, lowe recombination rate of photo-generated charger carrier. Upon these synergistic effects, the target hierarchical nanostructure shows significantly improved PEC performance and excellent photo-switching response with good reproducibility and stability. Corresponding photocurrent density and photon-to-current efficiency achieve 0.76 mA cm−2 and 0.50%, respectively, which show an enhancement of 1.70 and 1.32 times to those of the control one. This work provides a possible route for fabrication of TiO2 starting materials with decent efficiencies.

Enhanced Photoelectrochemical Performance of Co/TiO2Nanotubes Prepared by Electrodeposition

TiO2nanotube arrays (NTbs) have been widely used in the field of photocatalysis due to their large surface area, good controllability and superior electron transport properties. However, due to its wide bandgap (3.2[Formula: see text]eV), pure TiO2can only be excited by ultraviolet light ([Formula: see text][Formula: see text]nm), leading to low utilization of solar energy. Second, the high recombination rate of the photogenerated electrons and holes ([Formula: see text]/[Formula: see text] pair also reduces the quantum efficiency of TiO2. In order to realize the efficient photocatalytic activity of TiO2nanomaterials, it is necessary to design the TiO2nanomaterials to optimize the utilization of the solar spectrum. In this study, TiO2NTbs were obtained by the anodizing method using titanium foil, and a series of Co/TiO2NTbs were prepared by electrochemical deposition. The effects of the deposition voltage on the physical and photocatalytic properties of the Co/TiO2NTbs were investigated. Results found that the Co/TiO2NTbs had the highest photocurrent density 0.7[Formula: see text]mA/cm2at an electrodeposition time of 60[Formula: see text]s and a voltage of 1[Formula: see text]V, and the photoelectric conversion efficiency was 15.85%, which was approximately 2.8 times that of the pure TiO2NTbs. The degradation rate of Rhodamine B of the Co/TiO2NTbs in 120[Formula: see text]min was 76.3%, whereas that of the pure TiO2NTbs was only 48.7%. The forbidden bandwidth of the Co/TiO2NTbs was reduced to 3.02[Formula: see text]eV, whereas that of the pure TiO2NTbs was 3.2[Formula: see text]eV.

Enhanced strength-ductility-toughness synergy in an HSLA steel with multi-gradient ultrafine grained structure by adopting a two-stage rolling coupling inter-pass ultra-fast cooling process

In this work, a multi-gradient ultrafine grain (GUFG) structured high strength low alloy (HSLA) steel was successfully prepared by adopting a two-stage rolling coupling ultra-fast cooling process. The heterogeneous microstructure with gradients in grain size, shape, and texture across the thickness direction of the GUFG HSLA steel was characterized by large area electron backscattered diffraction (LA-EBSD) technique, and the quasi-static tensile properties, dynamic Charpy impact toughness, and its anisotropy were evaluated at ambient temperature. Results show that optimal matching of strength and ductility can be attained in the GUFG steel compared to the ultrafine grain (UFG) and coarse grain (CG) uniformed grain-sized structures. Furthermore, the GUFG specimens have a significantly enhanced toughness under dynamic impact loading, which was, respectively, 1.6 and 5.9 times that presented in uniform UFG and CG structures when impacted along the rolling direction. The refined grains and synergistic deformation of heterogeneous microstructures can contribute to the high strength without compromising ductility and toughness in GUFG specimens. In addition, the GUFG, UFG, and CG structures all exhibit obvious anisotropy in mechanical properties, which originate from distinct microstructure, texture, and delamination characteristics. This work not only reveals that the quasi-static/dynamic fracture resistance can be markedly improved by heterogenous structure-design strategies but also provide a realistic preparation technology for the exploitation of superior steel for engineering applications.

Process Development for Printed Copper With Surface Mount Devices on Inkjet Metallization

Abstract Printed electronics is a fastest growing and emerging technology that have shown much potential in several industries including automotive, wearables, healthcare, and aerospace. Its applications can be found not only in flexible but also in large area electronics. The technology provides an effective and convenient method to additively deposit conductive and insulating materials on any type of substrate. Despite its status, it is not without its challenges. Inkjet technology has gained much attention due to its low cost, low-material consumption, and capability for mass manufacturing. The preferred conductive metal of choice has been mostly silver due to its excellent electrical properties and ease in sintering. However, silver comes to be expensive than its counterpart copper. Since copper is prone to oxidation, much focus has been given toward photonic sintering that involves sudden burst of pulsed light at certain energy to sinter the copper nanoparticles. With this technique, only the printed material gets sintered in a matter of seconds without having a great impact on its substrate. With all the knowledge, there is still a large gap in the process side with copper where it is important to look how the print process affects the electrical and mechanical properties of copper. With the process developed, the resistivity of printed copper was found to be five times the bulk copper. In regards to adhesion to the polyimide film, mechanical shear load to failure was found to be within 15–20 gF. To demonstrate the complete process, commercial-off-the-shelf components are also mounted on the additively printed pads. Statistically, control charting technique is implemented to understand any process variation over long duration of prints.

Porous carbon nitride nanotubes efficiently promote two-electron O2 reduction for photocatalytic H2O2 production

Supramolecular self-assembly was used to synthesize uniform porous carbon nitride nanotubes successfully. The large specific surface area and superior electron transport performance are provided by nanotube structures. The temperature programmed desorption (TPD) test and the density functional theory (DFT) calculation indicate that porous carbon nitride nanotubes show a significant adsorption of O2. At the same time, the rotating ring-disk electrode (RRDE) experiments demonstrate that the porous carbon nitride nanotubes improved the selectivity of 2e- oxygen reduction reaction (ORR) (60% vs. 90%, 0.3 V vs. RHE) greatly. Consequently, the yield of H2O2 by porous carbon nitride nanotubes (93.89 μmol/L) is 2.4 times more than that of the original carbon nitride. Therefore, this research provides a feasible strategy for designing photocatalytic materials with high 2e- ORR selectivity.

Oxide thin-film transistors based on i-line stepper process for high PPI displays

Indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) with a 1 um channel length were successfully fabricated by i-line lithography with a stepper process, resulting in high throughput. The a-IGZO TFT with a channel length of 1 μm exhibits high mobility of 8.77 cm2/Vs with an on/off current ratio of >3 × 1010. The stepper lithography process is capable of defect-free patterning given its precise layer-to-layer alignment and high image resolutions of the types required for large-area high-PPI displays. Consequently, IGZO TFTs can be fabricated on an 8-inch wafer with only minor electrical property deviations in the turn-on voltage, mobility, and on/off ratio. These results indicate that i-line lithography with a stepper process is a promising process for use in cutting-edge large-area electronics industries.