Electronic Materials

Aerosol deposition (AD) is a simple, dry raw-powder deposition process in which the targeted film is formed by direct bombardment of accelerated starting powder onto the substrate surface at room temperature. Despite the increased interest in AD film formation, no work has been completed to systematically investigate the formation of dense zinc oxide (ZnO) films using the AD method and their optical properties. Therefore, this study was carried out to investigate the effect of AD gas flow rate on the formation of AD films and the optical properties of aerosol-deposited ZnO films. ZnO films with nanosized (<40 nm) crystallites were successfully deposited on FTO substrates at room temperature. A dense and uniform layer of aerosol-deposited ZnO films with a roughened surface was obtained without subsequent heat treatment. With the increase in the AD gas flow rate, the crystal size and the AD film’s thickness were reduced. The Raman spectroscopy verified that the thin film was of a ZnO wurtzite structure. The room temperature photoluminescence of the ZnO thin film produced strong visible emissions. The findings of this work demonstrated that AD can be an alternative technique for the rapid deposition of dense and thick ZnO films for optoelectronic applications. Full article

Wireless energy harvesting, a technique to generate direct current (DC) electricity from ambient wireless signals, has recently been featured as a potential solution to reduce the battery size, extend the battery life, or replace batteries altogether for wearable electronics. Unlike other energy harvesting techniques, wireless energy harvesting has a prominent advantage of ceaseless availability of ambient signals, but the common form of technology involves a major challenge of limited output power because of a relatively low ambient energy density. Moreover, the archetypal wireless energy harvesters are made of printed circuit boards (PCBs), which are rigid, bulky, and heavy, and hence they are not eminently suitable for body-worn applications from both aesthetic and comfort points of view. In order to overcome these limitations, textile-based wireless energy harvesting architectures have been proposed in the past decade. Being made of textile materials, this new class of harvesters can be seamlessly integrated into clothing in inherently aesthetic and comfortable forms. In addition, since clothing offers a large surface area, multiple harvesting units can be deployed to enhance the output power. In view of these unique and irreplaceable benefits, this paper reviews key recent progress in textile-based wireless energy harvesting strategies for powering body-worn electronics. Comparisons with other power harvesting technologies, historical development, fundamental principles of operation and techniques for fabricating textile-based wireless power harvesters are first recapitulated, followed by a review on the principal advantages, challenges, and opportunities. It is one of the purposes of this paper to peruse the current state-of-the-art and build a scientific knowledge base to aid further advancement of power solutions for wearable electronics. Full article

Lanthanum manganite (LMO) thin films were deposited by co-sputtering La and Mn targets in an Ar and O₂ gas mixture. The films were synthesized on silicon and fused silica substrates. The influences of thermal annealing on the structure, optical and electrical properties of LMO films were investigated. The results exhibited a correlation between these properties. In the amorphous state, an increase in annealing temperature improved the optical transmission and decreased the electrical capacitance. The beginning of crystallization at 600 °C was manifested by a strong increase in the capacitance and a decrease in the optical transmission. At higher annealing temperature, polycrystalline films were obtained with different optical and electrical characteristics. On the other hand, the annealed LMO films showed a photocurrent effect during exposure to a weak LED light. Full article

Among the plethora of soluble and easy processable organic semiconductors, 6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-P5) is one of the most promising materials for next-generation flexible electronics. However, based on the information reported in the literature, it is difficult to exploit in field-effect transistors the high-performance characteristics of this material. This article correlates the HMDS functionalization of the silicon substrate with the electrical characteristics of TIPS-P5-based bottom gate organic field-effect transistors (OFETs) and electrolyte-gated organic field-effect transistors (EGOFETs) fabricated over the same platform. TIPS-P5 transistors with a double-gate architecture were fabricated by simple drop-casting on Si/SiO₂ substrates, and the substrates were either functionalized with hexamethyldisilazane (HMDS) or left untreated. The same devices were characterized both as standard bottom-gate transistors and as (top-gate) electrolyte-gated transistors, and the results with and without HMDS treatment were compared. It is shown that the functionalization of the silicon substrate negatively influences EGOFETs performance, while it is beneficial for bottom-gate OFETs. Different device architectures (e.g., bottom-gate vs. top-gate) require specific evaluation of the fabrication protocols starting from the effect of the HMDS functionalization to maximize the electrical characteristics of TIPS-P5-based devices. Full article

The use of nonmetallic conductor materials in RF applications has recently become a highlighted issue when it comes to sustainability in the electronics industry, mainly because of the waste problems associated with heavy metals and the necessity of reducing and managing them. The replacement of metal in functional applications such as in electronics is therefore very important. Among these new materials, organic conductors are of great interest since they are, in general, biocompatible and biodegradable, allowing for the disposal of electronic devices, which reduces the negative environment impact caused by electronics waste. In this work, PEDOT:PSS and Carbon are investigated. Since these materials are available as conducting pastes or inks, the production of conducting patterns by printing techniques such as screen printing is possible, which can make the process less harmful to the environment, since it permits the use of organic substrates such as paper. In order to investigate the feasibility of these materials for RF signal transmission, screen printed PEDOT:PSS and Carbon transmission lines have been designed, fabricated and characterized. Results regarding conductivity, thickness, electric permittivity and S21 parameter are presented and will serve as a foundation for the development of further reaching applications utilizing organic materials. Full article

Currently, as the next-generation of display progresses—with high performance and high integration—the surface mounting technology of components is very important. In particular, in the case of flexible displays, such as rollable and bendable displays, ACF that connects wires to any curvature is essential. However, the conductive ball used inside the ACF has had problems with particle size and non-uniform metal coating. It was confirmed that the presence of solvent and oxygen, which are used in polymer synthesis, affects the sphere formation of polymer beads. By optimizing the factors affecting the polymer beads, a perfect spherical polymer bead was manufactured. In addition, the conductive ball manufacturing process was optimized by confirming the factors affecting the metal coating. The metal coating on the surface of the polymer bead was applied with a uniform thickness by considering the specific surface area and concentration of the conductive balls, and, through this optimized process, conductive balls for anisotropic conductive films with uniform size and metal thickness were obtained. Full article

This article will briefly review the progress of h-BN based solid-state metal semiconductor metal (MSM) neutron detectors. In the last decade, several groups have been working on hexagonal boron nitride (h-BN)-based solid-state neutron detectors. Recently, the detection efficiency of 59% has been reported. Efficient, low-cost neutron detectors made from readily available materials are essential for various applications. Neutron detectors are widely used to detect fissile materials and nuclear power plants for security applications. The most common and widely used neutron detectors are ³He based, which are sometimes bulky, difficult to transport, have high absorption length, need relatively high bias voltage (>1000 V), and have low Q-value (0.764 MeV). In addition, ³He is not a readily available material. Thus, there is a strong need to find an alternative detection material. The ¹⁰B isotope has a high neutron absorption cross-section, and it has been tested as a coating on the semiconducting materials. Due to the two-step process, neutron capture through ¹⁰B and then electron–hole pair generation in a typical semiconducting material, the efficiency of these devices is not up to the mark. The progress in h-BN based detectors requires a review to envision the further improvement in this technology. Full article

This work presents an examination and unification of fragmented data on spin polarization in half-metallic, ferrimagnetic oxides. It also includes well understood ferromagnetic metals for comparison. The temperature and disorder dependencies of the spin polarization are evaluated. Both the temperature dependence of the tunnel magnetoresistance and, for the very first time, its temperature coefficient are calculated based on the simplified Julliére model. The tunnel magnetoresistance in the magnetic tunnel junctions deteriorates due to the temperature dependence of the spin polarization the lower the Curie temperature is. As a result, magnetic tunnel junctions—consisting of ferromagnetic oxides with a Curie temperature not far above room temperature—are not promising for room temperature applications. Additionally, ferrimagnetic oxides possessing a Curie temperature below 650 K are not suitable for room temperature applications because of an unacceptable temperature coefficient exceeding −2%. Full article

In this work, the electrical properties of graphene papers were investigated with the aim of developing pressure sensor prototypes for measuring pressures up to 2 kPa. In order to determine which graphene paper would be the most suitable, three different types of graphene papers, synthesized by different routes, were prepared and electrically characterized. The results of electrical characterizations, in terms of electrical conductivity and sheet resistance of graphene papers, are presented and discussed. Prototypes of pressure sensors are proposed, using graphene papers obtained by chemical oxidation (graphene oxide and reduced graphene oxide) and by electrochemical exfoliation. The prototypes were tested in static compression/decompression tests in the working range of 0 kPa to 1.998 kPa. The compression/decompression sensitivity values observed in these prototype sensors ranged from 20.8% ΔR/kPa for graphene sensors obtained by electrochemical exfoliation to 110.7% ΔR/kPa for those prepared from graphene oxide obtained by chemical oxidation. More expressive sensitivity values were observed for the sensors fabricated from GO, intermediate values for those made of rGO, while prototypes made of EG showed lower sensitivity. Full article

The development of lithium-ion batteries (LIBs) based on current practice allows an energy density increase estimated at 10% per year. However, the required power for portable electronic devices is predicted to increase at a much faster rate, namely 20% per year. Similarly, the global electric vehicle battery capacity is expected to increase from around 170 GWh per year today to 1.5 TWh per year in 2030—this is an increase of 125% per year. Without a breakthrough in battery design technology, it will be difficult to keep up with their increasing energy demand. The objective of this investigation is to develop a design methodology to accelerate the LIB development through the integration of electro-chemical numerical simulations and machine learning algorithms. In this work, the Gaussian process (GP) regression model is used as a fast approximation of numerical simulation (conducted using Simcenter Battery Design Studio^®). The GP regression models are systematically updated through a multi-objective Bayesian optimization algorithm, which enables the exploration of innovative designs as well as the determination of optimal configurations. The results reported in this work include optimal thickness and porosities of LIB electrodes for several practical charge–discharge scenarios which maximize energy density and minimize capacity fade. Full article

The hot-carrier effect and hot-carrier dynamics in GaAs solar cell device performance were investigated. Hot-carrier solar cells based on the conventional operation principle were simulated based on the detailed balance thermodynamic model and the hydrodynamic energy transportation model. A quasi-equivalence between these two models was demonstrated for the first time. In the simulation, a specially designed GaAs solar cell was used, and an increase in the open-circuit voltage was observed by increasing the hot-carrier energy relaxation time. A detailed analysis was presented regarding the spatial distribution of hot-carrier temperature and its interplay with the electric field and three hot-carrier recombination processes: Auger, Shockley–Read–Hall, and radiative recombinations. Full article

The ferroelectric and pyroelectric properties of bismuth ferrite (BFO) epitaxial thin film have been investigated. The ferroelectric epitaxial thin layer has been deposited on strontium titanate (STO) (001) substrate by pulsed laser deposition, in a capacitor geometry using as top and bottom electrode a conductive oxide of strontium ruthenate (SRO). The structural characterizations performed by X-ray diffraction and atomic force microscopy demonstrate the epitaxial character of the ferroelectric thin film. The macroscopic ferroelectric characterization of BFO revealed a rectangular shape of a polarization-voltage loop with a remnant polarization of 30 μC/c m² and a coercive electric field of 633 KV/cm at room temperature. Due to low leakage current, the BFO capacitor structure could be totally pooled despite large coercive fields. A strong variation of polarization is obtained in 80–400 K range which determines a large pyroelectric coefficient of about 10⁻⁴ C/m² K deduced both by an indirect and also by a direct method. Full article

In this work, a defective commercial module with a rounded IV characteristic is analyzed in detail to identify the sources of its malfunction. The analysis of the module includes thermography images taken under diverse conditions, the IV response of the module obtained without any shadow, and shadowing one cell at a time, as recommended by the IEC 61215 Standard. Additionally, a direct measurement of the IV characteristic and resistance of single cells in the panel has been conducted to verify the isolation between the p and n areas. In parallel, theoretical cell and module behaviors are presented. In this frame, simulations show how cell mismatch can be the explanation to the rounded IV output of the solar panel under study. From the thermal images of the module, several localized hot spots related to failing cells have been revealed. During the present study, thermal breakdown is seen before avalanche breakdown in one of the cells, evidencing a hot spot. Not many papers have dealt with this problem, whereas we believe it is important to analyze the relationship between thermal breakdown and hot spotting in order to prevent it in the future, since hot spots are the main defects related to degradation of modern modules. Full article

Thin films of colloidal CZTS nanocrystals (NCs) synthesized using a “green” approach in water with a variation of the copper-to-tin ratio are investigated by Raman scattering, mid-infrared (molecular vibrations) and near-infrared (free carrier) absorption, X-ray photoemission spectroscopy (XPS), electrical conductivity, and conductive atomic force microscopy (cAFM). We determined the effect of the actual Cu content on the phonon spectra, electrical conductivity, and spectral parameters of the plasmon band. An increase in the electrical conductivity of the NC films upon annealing at 220 °C is explained by three factors: formation of a Cu_xS nanophase at the CZTS NC surface, partial removal of ligands, and improved structural perfection. The presence of the Cu_xS phase is concluded to be the determinant factor for the CZTS NC film conductivity. Cu_xS can be reliably detected based on the analysis of the modified Auger parameter of copper, derived from XPS data and corroborated by Raman spectroscopy data. Partial removal of the ligand is concluded from the agreement of the core-level XPS and vibrational IR spectra. The degree of lattice perfection can be conveniently assessed from the Raman data as well. Further important information derived from a combination of photoelectron and optical data is the work function, ionization potential, and electron affinity of the NC films. Full article

This study aims to discuss the combined theoretical and experimental results of elastic properties of tungsten trioxide films supported on Quartz (YX)/45°/10° resonator to form surface acoustic wave (SAW) devices. The SAW systems with different thicknesses of WO₃ thin films were imaged and structurally characterized by X-ray diffraction, atomic force, and transmission electron microscopy. The deposited WO₃ films (100, 200, and 300 nm of thickness) crystallized in a single monoclinic phase. The acoustoelectric properties of the SAW system were obtained by combining theoretical simulations with experimental measurements. The modeling of the SAW devices has been performed by the finite element and boundary element methods (FEM/BEM). The elastic constants of the films at room temperature were assessed via electrical admittances experiments in light of theoretical calculations. The gravimetric effect of the deposited layers is observed by a shift of the resonance frequency to lower values as the thickness of the films increases. Moreover, the acoustic losses are affected by the dielectric losses of the WO₃ films while the resonant frequency decreases almost linearly. SAW devices revealed strong displacement fields with low acoustic losses as a function of WO₃ thicknesses. For all the deposited layers, the measured Young’s moduli and Poisson’s ratios are 8 GPa and 0.5, respectively. Full article

In this review, we provide an overview of the most common majority and minority charge carrier traps in n-type 4H-SiC materials. We focus on the results obtained by different applications of junction spectroscopy techniques. The basic principles behind the most common junction spectroscopy techniques are given. These techniques, namely, deep-level transient spectroscopy (DLTS), Laplace DLTS (L-DLTS), and minority carrier transient spectroscopy (MCTS), have led to recent progress in identifying and better understanding the charge carrier traps in n-type 4H-SiC materials. Full article

This work shows a correlation between light reflectance, absorption, and morphologies of series of bismuth manganate–lead titanate, (1 − x) BM–x PT, (x = 0.00, 0.02, 0.04, 0.08, 0.12, 0.16, 0.24, 1.00) ceramics composite. Low reflectance in the Vis-NIR range corresponds to ‘black mirror’ features. The modified Kubelka-Munk function applied to measured visible-near infrared (Vis-NIR) diffuse reflectance enabled the estimation of the energy gaps magnitude of the order of 1.0–1.2 eV for BM-PT. Histograms of grains, obtained using a scanning electron microscope, enabled finding the correlation between grains size, reflectance magnitude, and PT content. The magnitude of energy gaps was attributed to electronic structure bands modified by crystal lattice disorder and oxygen vacancies. Full article

Computational ghost imaging, as an alternative photoelectric imaging technology, uses a single-pixel detector with no spatial resolution to capture information and reconstruct the image of a scene. Due to its essentially temporal measurement manner, improving the image frame rate is always a major concern in the research of computational ghost imaging technology. By taking advantage of the fast switching time of LED, an LED array was developed to provide a structured illumination light source in our work, which significantly improves the structured illumination rate in the computational ghost imaging system. The design of the LED array driver circuit presented in this work makes full use of the LED switching time and achieves a pattern displaying rate of 12.5 MHz. Continuous images with 32 × 32 pixel resolution are reconstructed at a frame rate of 25,000 fps, which is approximately 500 times faster than what a universally used digital micromirror device can achieve. The LED array presented in this work can potentially be applied to other techniques requiring high-speed structured illumination, such as fringe 3D profiling and array-based LIFI. Full article