Enhanced Switching Reliability of Sol–Gel-Processed Y2O3 RRAM Devices Based on Y2O3 Surface Roughness-Induced Local Electric Field

Sol–gel-processed Y₂O₃ films were used as active channel layers for resistive random access memory (RRAM) devices. The fabricated ITO/Y₂O₃/Ag RRAM devices exhibited the properties of conventional bipolar memory devices. A triethylamine stabilizer with a high vapor pressure and low surface tension was added to realize the local electric field area. During drying and high-temperature post-annealing processes, the large convective flow enhanced the surface elevation, and the increased –OH groups accelerated the hydrolysis reaction and aggregation. These phenomena afforded Y₂O₃ films with an uneven surface morphology and an increased surface roughness. The increased roughness of the Y₂O₃ films attributable to the triethylamine stabilizer enhanced the local electrical field, improved device reliability, and achieved successful repetition of the switching properties over an extended period.     

Effects of Electrodes on the Switching Behavior of Strontium Titanate Nickelate Resistive Random Access Memory

Strontium titanate nickelate (STN) thin films on indium tin oxide (ITO)/glass substrate were synthesized using the sol-gel method for resistive random access memory (RRAM) applications. Aluminum (Al), titanium (Ti), tungsten (W), gold (Au) and platinum (Pt) were used as top electrodes in the STN-based RRAM to probe the switching behavior. The bipolar resistive switching behavior of the set and reset voltages is in opposite bias in the Al/STN/ITO and Pt/STN/ITO RRAMs, which can be partly ascribed to the different work functions of top electrodes in the ITO. Analyses of the fitting results and temperature-dependent performances showed that the Al/STN/ITO switching was mainly attributed to the absorption/release of oxygen-based functional groups, whereas the Pt/STN/ITO switching can be associated with the diffusion of metal electrode ions. The Al/STN/ITO RRAM demonstrated a high resistance ratio of >10⁶ between the high-resistance state (HRS) and the low-resistance state (LRS), as well as a retention ability of >10⁵ s. Furthermore, the Pt/STN/ITO RRAM displayed a HRS/LRS resistance ratio of >10³ and a retention ability of >10⁵ s.     

Quasi-Continuous Network Structure Greatly Improved the Anti-Arc-Erosion Capability of Ag/Y2O3 Electrical Contacts

Ag/Y₂O₃ has excellent potential to replace Ag/CdO as the environmentally friendly electrical contact material. Using spherical Y₂O₃ as the starting material, Ag/Y₂O₃ contacts with a quasi-continuous network structure were successfully fabricated by a low-energy ball milling treatment. The mean size of Y₂O₃ used ranged from 243 to 980 nm. Due to the differences in the size of Y₂O₃, Ag/Y₂O₃ contacts had different primitive microstructures, thereby exhibiting distinctive anti-arc-erosion capabilities. Ag/Y₂O₃ contact prepared using 243 nm Y₂O₃ showed the best anti-arc-erosion capability and the most outstanding electrical performance measures, such as low contact resistance, less mass transfer, and no failure up to 10⁵ cycle times. The quasi-continuous network structure formed in the micro-scale was responsible for the excellent electrical performance. The short distance between Y₂O₃ particles in the network promoted the cathode arc motion, and thus alleviated the localized erosion. The results obtained herein may inspire further attempts to design electrical contacts rationally.     

Red Y2O3:Eu-Based Electroluminescent Device Prepared by Atomic Layer Deposition for Transparent Display Applications

Y₂O_3:Eu is a promising red-emitting phosphor owing to its high luminance efficiency, chemical stability, and non-toxicity. Although Y₂O₃:Eu thin films can be prepared by various deposition methods, most of them require high processing temperatures in order to obtain a crystalline structure. In this work, we report on the fabrication of red Y₂O₃:Eu thin film phosphors and multilayer structure Y₂O₃:Eu-based electroluminescent devices by atomic layer deposition at 300 °C. The structural and optical properties of the phosphor films were investigated using X-ray diffraction and photoluminescence measurements, respectively, whereas the performance of the fabricated device was evaluated using electroluminescence measurements. X-ray diffraction measurements show a polycrystalline structure of the films whereas photoluminescence shows emission above 570 nm. Red electroluminescent devices with a luminance up to 40 cd/m² at a driving frequency of 1 kHz and an efficiency of 0.28 Lm/W were achieved.     

Improvement of Resistive Switching Performance in Sulfur-Doped HfOx-Based RRAM

In order to improve the electrical performance of resistive random access memory (RRAM), sulfur (S)-doping technology for HfOx-based RRAM is systematically investigated in this paper. HfOx films with different S-doping contents are achieved by atmospheric pressure chemical vapor deposition (APCVD) under a series of preparation temperatures. The effect of S on crystallinity, surface topography, element composition of HfOx thin films and resistive switching (RS) performance of HfOx-based devices are discussed. Compared with an undoped device, the V_SET/V_RESET of the S-doped device with optimal S content (~1.66 At.%) is reduced, and the compliance current (Icc) is limited from 1 mA to 100 μA. Moreover, it also has high uniformity of resistance and voltage, stable endurance, good retention characteristics, fast response speed (SET 6.25 μs/RESET 7.50 μs) and low energy consumption (SET 9.08 nJ/RESET 6.72 nJ). Based on X-ray photoelectron spectroscopy (XPS) data and fitting of the high/low resistance state (HRS/LRS) conduction behavior, a switching mechanism is considered to explain the formation and rupture of conductive filaments (CFs) composed of oxygen vacancies in undoped and S-doped HfOx-based devices. Doping by sulfur is proposed to introduce the appropriate concentration oxygen vacancies into HfOx film and suppress the random formation of CFs in HfOx-based device, and thus improve the performance of the TiN/HfOx/ITO device.     

Resistance Switching Effect of Memory Device Based on All-Inorganic Cspbbri2 Perovskite

In this study, the CsPbBrI₂ perovskite film was prepared by the preparation of the sol-gel and the spin-coating method, and the cubic lattice was stabilized by introducing Br⁺ into the CsPbI₃ film, which solved the problem of instability of the traditional perovskite phase. Based on the CsPbBrI₂ perovskite film, the Ag/CsPbBrI₂/ITO memory device with a resistance switching effect was prepared. The morphology and phase compositions of the film were analyzed by scanning electron microscope and X-ray diffraction. The non-volatile and repeatable resistance switching effect of the Ag/CsPbBrI₂/ITO memory device was measured under open-air conditions. The experimental results show that the surface of the CsPbBrI₂ perovskite film is uniform and dense, and the Ag/CsPbBrI₂/ITO memory device has an order of magnitude resistance-on-off ratio after 500 cycles of cyclic voltage. This study shows that Ag/CsPbBrI₂/ITO memory devices based on CsPbBrI₂ perovskite films have potential applications in the field of non-volatile memory devices. At the same time, the transient properties of the CsPbBrI₂ film that can quickly dissolve in deionized water make it potentially useful in short-period data storage units and implantable electronic devices with human or environmental sensors.     

Fabrication of Multiferroic Co-Substituted BiFeO3 Epitaxial Films on SrTiO3 (100) Substrates by Radio Frequency Magnetron Sputtering

The 10 at.% Co-substituted BiFeO₃ films (of thickness 50 nm) were successfully prepared by radio frequency (r.f.) magnetron sputtering on SrTiO₃ (100) substrates with epitaxial relationships of [001](001)Co-BiFeO₃//[001](001)SrTiO₃. In this study, a single phase Co-substituted BiFeO₃ epitaxial film was fabricated by r.f. magnetron sputtering. Sputtering conditions such as Ar, O₂ gas pressure, annealing temperature, annealing atmosphere, and sputtering power were systematically changed. It was observed that a low Ar gas pressure and low sputtering power is necessary to suppress the formation of the secondary phases of BiO_x. The Co-substituted BiFeO₃ films were crystalized with post-annealing at 600 °C in air. The process window for single phase films is narrower than that for pure BiFeO₃ epitaxial films. By substituting Fe with Co in BiFeO₃, the magnetization at room temperature increased to 20 emu/cm³. This result suggests that Co-substituted BiFeO₃ films can be used in spin-filter devices.     

Thermal Annealing Effects of V2O5 Thin Film as an Ionic Storage Layer for Electrochromic Application

A vanadium pentoxide (V₂O₅) thin film with thermal annealing as an ionic storage layer for electrochromic devices is presented in our study. The V₂O₅ thin film was deposited on an ITO glass substrate by an RF magnetron sputtering. The electrochromic properties of the film were evaluated after various thermal annealing temperatures. The structural analysis of the film was observed by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), and atomic force microscopy (AFM). The structure of the V₂O₅ thin film transformed from an amorphous to polycrystalline structure with directions of (110) and (020) after 400 °C thermal annealing. The electrochromic properties of the film improved compared with the unannealed V₂O₅ thin film. We obtained a charge capacity of 97.9 mC/cm² with a transparent difference ΔT value of 31% and coloration efficiency of 6.3 cm²/C after 400 °C thermal annealing. The improvement was due to the polycrystalline orthorhombic structure formation of V₂O₅ film by the rearrangement of atoms from thermal energy. Its laminate structure facilitates Li⁺ ion intercalation and increases charge capacity and transparent difference.     

Nanocluster-Based Ultralow-Temperature Driven Oxide Gate Dielectrics for High-Performance Organic Electronic Devices

The development of novel dielectric materials with reliable dielectric properties and low-temperature processibility is crucial to manufacturing flexible and high-performance organic thin-film transistors (OTFTs) for next-generation roll-to-roll organic electronics. Here, we investigate the solution-based fabrication of high-k aluminum oxide (Al₂O₃) thin films for high-performance OTFTs. Nanocluster-based Al₂O₃ films fabricated by highly energetic photochemical activation, which allows low-temperature processing, are compared to the conventional nitrate-based Al₂O₃ films. A wide array of spectroscopic and surface analyses show that ultralow-temperature photochemical activation (<60 °C) induces the decomposition of chemical impurities and causes the densification of the metal-oxide film, resulting in a highly dense high-k Al₂O₃ dielectric layer from Al-13 nanocluster-based solutions. The fabricated nanocluster-based Al₂O₃ films exhibit a low leakage current density (<10⁻⁷ A/cm²) at 2 MV/cm and high dielectric breakdown strength (>6 MV/cm). Using this dielectric layer, precisely aligned microrod-shaped 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C8-BTBT) single-crystal OTFTs were fabricated via solvent vapor annealing and photochemical patterning of the sacrificial layer.     

Applied IrO2 Buffer Layer as a Great Promoter on Ti-Doping V2O5 Electrode to Enhance Electrochromic Device Properties

Electrochromic devices (ECDs) are a promising material for smart windows that are capable of transmittance variation. However, ECDs are still too expensive to achieve a wide market reach. Reducing fabrication cost remains a challenge. In this study, we inserted an IrO₂ buffer layer on Ti-doped V₂O₅ (Ti:V₂O₅) as a counter electrode using various Ar/O₂ gas flow ratios (1/2, 1/2.5, 1/3 and 1/3.5) in the fabrication process. The buffered-ECD resulted in a larger cyclic voltammetry (CV) area and the best surface average roughness (Ra = 3.91 nm) to promote electrochromic performance. It was fabricated using the low-cost, fast deposition process of vacuum cathodic arc plasma (CAP). This study investigates the influence of the IrO₂ buffer/Ti:V₂O₅ electrode on ECD electrochemical and optical properties, in terms of color efficiency (CE) and cycle durability. The buffered ECD (glass/ITO/WO₃/liquid electrolyte/IrO₂ buffer/Ti:V₂O₅/ITO/glass) demonstrated excellent optical transmittance modulation; ∆T = 57% (from T_bleaching (67%) to T_coloring (10%)) at 633 nm, which was higher than without the buffer (ITO/WO₃/liquid electrolyte/Ti:V₂O₅/ITO) (∆T = 36%). In addition, by means of an IrO₂ buffer, the ECD exhibited high coloration efficiency of 96.1 cm²/mC and good durability, which decayed by only 2% after 1000 cycles.     

The ZnO-In2O3 Oxide System as a Material for Low-Temperature Deposition of Transparent Electrodes

The development of optoelectronic devices based on flexible organic substrates substantially decreases the possible process temperatures during all stages of device manufacturing. This makes it urgent to search for new transparent conducting oxide (TCO) materials, cheaper than traditional indium-tin oxide (ITO), for the low-temperature deposition of transparent electrodes, a necessary component of most optoelectronic devices. The article presents the results of a vertically integrated study aimed at the low-temperature production of TCO thin films based on a zinc-indium oxide (ZIO) system with acceptable functional characteristics. First, dense and conducting ceramic targets based on the (100-x) mol% (ZnO) + x mol% (In₂O₃) system (x = 0.5, 1.5, 2.5, 5.0, and 10.0) were synthesized by the spark plasma sintering method. The dependences of the microstructure and phase composition of the ZIO ceramic targets on the In₂O₃ content have been studied by powder X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy methods. Then, a set of ZIO thin films with different Zn/In ratios were obtained on unheated glass substrates by direct current (dc) magnetron sputtering of the sintered targets. Complex studies of microstructure, electrical and optical properties of the deposited films have revealed the presence of an optimal doping level (5 mol% In₂O₃) of the ZIO target at which the deposited TCO films, in terms of the combination of their electrical and optical properties, become comparable to the widely used expensive ITO.     

Flexible Memory Device Composed of Metal-Oxide and Two-Dimensional Material (SnO2/WTe2) Exhibiting Stable Resistive Switching

Two-terminal, non-volatile memory devices are the fundamental building blocks of memory-storage devices to store the required information, but their lack of flexibility limits their potential for biological applications. After the discovery of two-dimensional (2D) materials, flexible memory devices are easy to build, because of their flexible nature. Here, we report on our flexible resistive-switching devices, composed of a bilayer tin-oxide/tungsten-ditelluride (SnO₂/WTe₂) heterostructure sandwiched between Ag (top) and Au (bottom) metal electrodes over a flexible PET substrate. The Ag/SnO₂/WTe₂/Au flexible devices exhibited highly stable resistive switching along with an excellent retention time. Triggering the device from a high-resistance state (HRS) to a low-resistance state (LRS) is attributed to Ag filament formation because of its diffusion. The conductive filament begins its development from the anode to the cathode, contrary to the formal electrochemical metallization theory. The bilayer structure of SnO₂/WTe₂ improved the endurance of the devices and reduced the switching voltage by up to 0.2 V compared to the single SnO₂ stacked devices. These flexible and low-power-consumption features may lead to the construction of a wearable memory device for data-storage purposes.     

Synthesis of Ni/Y2O3 Nanocomposite through USP and Lyophilisation for Possible Use as Coating

The Ni/Y₂O₃ catalyst showed high catalytic activity. Based on this, the aim of this study was to create Ni/Y₂O₃ nanocomposites powder with two innovative technologies, Ultrasonic Spray Pyrolysis (USP) and lyophilisation. In the USP process, thermal decomposition of the generated aerosols in an N₂/H₂ reduction atmosphere caused a complete decomposition of the nickel (II) nitrate to elemental Ni, which became trapped on the formed Y₂O₃ nanoparticles. The Ni/Y₂O₃ nanocomposite particles were captured via gas washing in an aqueous solution of polyvinylpyrrolidone (PVP) in collection bottles. PVP was chosen for its ability to stabilise nano-suspensions and as an effective cryoprotectant. Consequently, there was no loss or agglomeration of Ni/Y₂O₃ nanocomposite material during the lyophilisation process. The Ni/Y₂O₃ nanocomposite powder was analysed using ICP-MS, SEM-EDX, and XPS, which showed the impact of different precursor concentrations on the final Ni/Y₂O₃ nanocomposite particle composition. In a final step, highly concentrated Ni/Y₂O₃ nanocomposite ink (Ni/Y₂O₃ > 0.140 g/mL) and test coatings from this ink were prepared by applying them on a white matte photo paper sheet. The reflection curve of the prepared Ni/Y₂O₃ nanocomposite coating showed a local maximum at 440 nm with a value of 39% reflection. Given that Ni is located on the surface of the Ni/Y₂O₃ nanocomposite in the elemental state and according to the identified properties, tests of the catalytic properties of this coating will be performed in the future.     

Fabrication of Cu2ZnSnS4 Light Absorber Using a Cost-Effective Mechanochemical Method for Photovoltaic Applications

In the present study, we adopt an easy and cost-effective route for preparing Cu₂ZnSnS₄ (CZTS)-absorber nanoparticles by a mechanochemical method using non-toxic and environmentally benign solvents (butanol, methyl ethyl ketone, and ethanol). The gram-scale synthesis of absorber nanoparticles was achieved in a non-hazardous, zero-waste process without using high-vacuum equipment. The effects of annealing and Na incorporation on the properties of spin-coated CZTS thin films were scrutinized. The deposited samples showed kesterite crystal structure and single phase. The morphological results revealed an improvement in the surface morphology after annealing. The optical bandgaps of the thin films lied in the range of 1.50–1.57 eV with p-type nature. Finally, photovoltaic devices were fabricated, and their cell performance parameters were studied. An efficiency of 0.16% was observed. The present study provides a potential route for the cost-effective fabrication of CZTS-based photovoltaic devices.     

Effects of Insertion of Ag Mid-Layers on Laser Direct Ablation of Transparent Conductive ITO/Ag/ITO Multilayers: Role of Effective Absorption and Focusing of Photothermal Energy

From the viewpoint of the device performance, the fabrication and patterning of oxide–metal–oxide (OMO) multilayers (MLs) as transparent conductive oxide electrodes with a high figure of merit have been extensively investigated for diverse optoelectronic and energy device applications, although the issues of their general concerns about possible shortcomings, such as a more complicated fabrication process with increasing cost, still remain. However, the underlying mechanism by which a thin metal mid-layer affects the overall performance of prepatterned OMO ML electrodes has not been fully elucidated. In this study, indium tin oxide (ITO)/silver (Ag)/ITO MLs are fabricated using an in-line sputtering method for different Ag thicknesses on glass substrates. Subsequently, a Q-switched diode-pumped neodymium-doped yttrium vanadate (Nd:YVO₄, λ = 1064 nm) laser is employed for the direct ablation of the ITO/Ag/ITO ML films to pattern ITO/Ag/ITO ML electrodes. Analysis of the laser-patterned results indicate that the ITO/Ag/ITO ML films exhibit wider ablation widths and lower ablation thresholds than ITO single layer (SL) films. However, the dependence of Ag thickness on the laser patterning results of the ITO/Ag/ITO MLs is not observed, despite the difference in their absorption coefficients. The results show that the laser direct patterning of ITO/Ag/ITO MLs is primarily affected by rapid thermal heating, melting, and vaporization of the inserted Ag mid-layer, which has considerably higher thermal conductivity and absorption coefficients than the ITO layers. Simulation reveals the importance of the Ag mid-layer in the effective absorption and focusing of photothermal energy, thereby supporting the experimental observations. The laser-patterned ITO/Ag/ITO ML electrodes indicate a comparable optical transmittance, a higher electrical current density, and a lower resistance compared with the ITO SL electrode.     

One-Step Etching Characteristics of ITO/Ag/ITO Multilayered Electrode in High-Density and High-Electron-Temperature Plasma

This paper presents the dry etching characteristics of indium tin oxide (ITO)/Ag/ITO multilayered thin film, used as a pixel electrode in a high-resolution active-matrix organic light-emitting diode (AMOLED) device. Dry etching was performed using a combination of H₂ and HCl gases in a reactive ion etching system with a remote electron cyclotron resonance (ECR) plasma source, in order to achieve high electron temperature. The effect of the gas ratio (H₂/HCl) was closely observed, in order to achieve an optimal etch profile and an effective etch process, while other parameters—such as the radio frequency (RF) power, ECR power, chamber pressure, and temperature—were fixed. The optimized process, with an appropriate gas ratio, constitutes a one-step serial dry etch solution for ITO and Ag multilayered thin films.     

Fabrication of Ga2O3 Schottky Barrier Diode and Heterojunction Diode by MOCVD

In this article, we reported on a Ga₂O₃-based Schottky barrier diode and heterojunction diode from MOCVD. The Si-doped n-type Ga₂O₃ drift layer, grown by MOCVD, exhibited high crystal quality, flat surfaces, and uniform doping. The distribution of unintentional impurities in the films was studied. Then nickel Schottky barrier diode and p-NiO/n-Ga₂O₃ heterojunction diode were fabricated and measured. Without any electric field management structure, the Schottky barrier diode and heterojunction diode have specific resistances of 3.0 mΩ·cm² and 6.2 mΩ·cm², breakdown voltages of 380 V and 740 V, thus yielding power figures of merit of 48 MW·cm⁻² and 88 MW·cm⁻², respectively. Besides, both devices exhibit a current on/off ratio of more than 10¹⁰. This shows the prospect of MOCVD in power device manufacture.     

A Review on Resistive Switching in High-k Dielectrics: A Nanoscale Point of View Using Conductive Atomic Force Microscope

Metal-Insulator-Metal (MIM) structures have raised as the most promising configuration for next generation information storage, leading to great performance and fabrication-friendly Resistive Random Access Memories (RRAM). In these cells, the memory concept is no more based on the charge storage, but on tuning the electrical resistance of the insulating layer by applying electrical stresses to reach a high resistive state (HRS or “0”) and a low resistive state (LRS or “1”), which makes the memory point. Some high-k dielectrics show this unusual property and in the last years high-k based RRAM have been extensively analyzed, especially at the device level. However, as resistance switching (in the most promising cells) is a local phenomenon that takes place in areas of ~100 nm², the use of characterization tools with high lateral spatial resolution is necessary. In this paper the status of resistive switching in high-k materials is reviewed from a nanoscale point of view by means of conductive atomic force microscope analyses.     

Fabrication of Single-Phase Manganese Oxide Films by Metal-Organic Decomposition

Here, single-phase Mn₂O₃ and Mn₃O₄ films are successfully fabricated by a facile solution process based on metal-organic decomposition (MOD), for the first time. A formulated manganese 2-ethylhexanoate solution was used as an MOD precursor for the preparation of manganese oxide films. The difference in thermal decomposition behavior of precursor solution in air and inert atmospheres was observed, indicating that the calcination atmosphere is the main factor for controlling the valence of manganese oxide films. Significantly, the solution-coated films on substrates are found to be transformed into single-phase Mn₂O₃ and Mn₃O₄ films when they are calcinated under air and inert atmosphere, respectively. The film crystallinity was improved with increasing calcination temperature for both Mn₂O₃ and Mn₃O₄ films. In particular, it is noted that the grains of Mn₂O₃ film were somewhat linearly grown in air, while those of Mn₃O₄ film exhibited the drastic growth in Ar with an increase of calcination temperature.     

Statistical Analysis of Uniform Switching Characteristics of Ta2O5-Based Memristors by Embedding In-Situ Grown 2D-MoS2 Buffer Layers

A memristor based on emerging resistive random-access memory (RRAM) is a promising candidate for use as a next-generation neuromorphic computing device which overcomes the von Neumann bottleneck. Meanwhile, due to their unique properties, including atomically thin layers and surface smoothness, two-dimensional (2D) materials are being widely studied for implementation in the development of new information-processing electronic devices. However, inherent drawbacks concerning operational uniformities, such as device-to-device variability, device yield, and reliability, are huge challenges in the realization of concrete memristor hardware devices. In this study, we fabricated Ta₂O₅-based memristor devices, where a 2D-MoS₂ buffer layer was directly inserted between the Ta₂O₅ switching layer and the Ag metal electrode to improve uniform switching characteristics in terms of switching voltage, the distribution of resistance states, endurance, and retention. A 2D-MoS₂ layered buffer film with a 5 nm thickness was directly grown on the Ta₂O₅ switching layer by the atomic-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) method, which is highly uniform and provided a superior yield of 2D-MoS₂ film. It was observed that the switching operation was dramatically stabilized via the introduction of the 2D-MoS₂ buffer layer compared to a pristine device without the buffer layer. It was assumed that the difference in mobility and reduction rates between Ta₂O₅ and MoS₂ caused the narrow localization of ion migration, inducing the formation of more stable conduction filament. In addition, an excellent yield of 98% was confirmed while showing cell-to-cell operation uniformity, and the extrinsic and intrinsic variabilities in operating the device were highly uniform. Thus, the introduction of a MoS₂ buffer layer could improve highly reliable memristor device switching operation.