ZrO2 Layer Research Articles

Low Temperature Sol-Gel Processed Zirconium Oxide Based Transparent Resistive Random Access Memory Devices

In this work, solution-processed ZrO2-based resistive random-access memory (RRAM) device with ITO (Indium Tin Oxide) as a bottom electrode (BE) was fabricated at a low thermal budget by sol-gel spin coating technique. The grown devices (ZrO2/ITO) were found to be amorphous by XRD measurements and exhibit 80% transmittance in the visible region. The resistive switching characteristics of solution-processed ZrO2 thin films were investigated. The W/ZrO2/ITO device exhibits good cyclic endurance with an on-off ratio (~10) and reliable switching and good retention at room temperature. The conduction mechanism for the low resistance state is ohmic, whereas the conduction mechanism of the high resistance state is ohmic at low applied voltages, while a space charge limited conduction (SCLC) at the high applied voltages. The combined ohmic and space charge limited conduction mechanisms together indicate that the RS behavior in the ZrO2 layer is due to the formation and rupture of conducting filaments. Results suggest that solution-processed ZrO2 has great potential to develop transparent and flexible resistive random access memory devices.

Structure and energetics of ZrC(100)||c-ZrO2(001) interface: A combination of experiments, finite temperature molecular dynamics, periodic DFT and atomistic thermodynamic modeling

The oxidation process of ZrC is very important as it affects its initial excellent mechanical and physical properties. ZrC is an ultra-high temperature ceramic, but forms low refractory oxides at lower temperatures of 500–600 °C. To develop core/shell materials by coating the ZrC surface with another material that forms protective layers on ZrC and prevents it from oxidation (such as SiC), there is the need to study and characterize the oxidized layer surrounding ZrC particles. XPS, ToF-SIMS, TEM-ED and EDX analyses were used to investigate the covering oxidized layer, and polycrystalline ZrO2(mainly cubic phase) was identified. Some traces of the tetragonal phase are observed to be present as shells around the ZrC particles with a thickness of about 4 nm on the average. Periodic DFT was subsequently used to characterize the interface formed between ZrC(100) and c-ZrO2(001) phases. A strong interface was noticed mainly with charge transfer from Zr (c-ZrO2 side) at the interface to O and C (ZrC side) atoms at the interface. The interfacial properties are local to only the first and second layers of ZrO2, and not on the third and fourth layers of ZrO2, as Bader charge analysis revealed substantial charge transfer at the interface region with no charge redistribution in the second ZrO2 layer and subsequent bulk layers. The main physical quantity, ideal work of adhesion (Wad), used to characterize the interface, remains quite constant for all ZrO2 layers, and converges at three layers of ZrO2. The interfacial bonds formed are observed to be stronger than the free surfaces in the corresponding ZrC and c-ZrO2 used to generate the interface.

The Contrasting Impacts of the Al2O3 and Y2O3 Insertion Layers on the Crystallization of ZrO2 Films for Dynamic Random Access Memory Capacitors

AbstractThis study examines the influences of the Al2O3 and Y2O3 insertion layers (ILs) on the structural and electrical features of ZrO2 thin films for their application to dynamic random access memory capacitors. The ultra‐thin Al2O3 IL (0.1–0.2 nm) dissolves into the ZrO2 layers, which causes the top and bottom portions of the ZrO2 film to merge and have smaller lattice parameters. However, the thicker Al2O3 IL (>≈0.4 nm) forms a continuous layer and separates the top and bottom portions of the ZrO2 film. Interestingly, the diffusion of Al does not occur in this case. Overall, the dielectric constant (κ) of the ZrO2/Al2O3/ZrO2 film is lower than that of the undoped ZrO2 film due to the involvement of the low‐κ Al2O3 IL. In contrast, the Y2O3 IL does not interfere with the grain growth of ZrO2, rendering the continuous ZrO2 grain formation throughout the entire film thickness despite the presence of the continuous region with a higher Y‐concentration. The most crucial finding is that the Y‐doping significantly decreases the leakage current without sacrificing the dielectric constant. This leakage current decrease can be ascribed to the p‐type doping effect of Y ions in the n‐type ZrO2.

Atomic-resolved structural and electric field analysis of the passivation interface of MIS-HEMTs

The passivation interfaces of GaN-based MIS-HEMTs with Si3N4 and ZrO2/Si3N4 bilayers were investigated through atomic resolution scanning transmission electron microscope–energy dispersive spectroscopy–differential phase contrast microscopy methods. It is found that the Si3N4/GaN interface exhibits atomic disorder fluctuation, and the GaN surface is discontinuous at the depth of 1–2 atomic layers. An oxide layer of ∼2 nm is formed at the ZrO2/GaN interface, and the GaN surface is atomically flat. Furthermore, the local minimum of the potential is located at the Si3N4/GaN interface, while it is distributed in the GaN side at the ZrO2/GaN interface. The electric field or potential distribution is affected by the crystal orientation of the polycrystalline ZrO2 layer. Finally, the difference in passivation mechanism is discussed.

Mechanical Behavior and Thermal Stability of (AlCrTiZrMo)N/ZrO2 Nano-Multilayered High-Entropy Alloy Film Prepared by Magnetron Sputtering

A new type of high-entropy alloy, a nitride-based (AlCrTiZrMo)N/ZrO2 nano-multilayered film, was designed to investigate the effect of ZrO2 layer thickness on the microstructure, mechanical properties, and thermal stability. The results show that when the thickness of the ZrO2 layer is less than 0.6 nm, it can be transformed into cubic-phase growth under the template effect of the (AlCrTiZrMo)N layer, resulting in an increased hardness. The (AlCrTiZrMo)N/ZrO2 film with a ZrO2 layer thickness of 0.6 nm has the highest hardness and elastic modulus of 35.1 GPa and 376.4 GPa, respectively. As the thickness of the ZrO2 layer further increases, ZrO2 cannot maintain the cubic structure, and the epitaxial growth interface is destroyed, resulting in a decrease in hardness. High-temperature annealing treatments indicate that the mechanical properties of the film decrease slightly after annealing at less than 900 °C for 30 min, while the mechanical properties decrease significantly after annealing for 30 min at 1000–1100 °C. The hardness and elastic modulus after annealing at 900 °C are still 24.5 GPa and 262.3 GPa, showing excellent thermal stability. This conclusion verifies the “template” effect of the nano-multilayered film, which improves the hardness and thermal stability of the high-entropy alloy.

Grain growth limitation in the monolayer ZrB2–SiC coating above 1700 °C

The cracking behavior along the interface (surface ZrO2 layer and unoxidized ZrB2–SiC layer) in the thermally sprayed ZrB2–SiC coating above 1700 °C was investigated by cyclic ablation tests (2.4 MW/m2). Experiment and simulation results show that the rapid growth of surface ZrO2 grains will greatly promote the interfacial micropores development until the formation of inter-laminar cracks. To address this issue, the laminated ZrB2–SiC/ZrO2 coating was prepared. The ZrO2 interface layer effectively restrained surface ZrO2 grain growth and improved the structural integrity by hindering the diffusion of liquid B2O3 and SiO2 towards the surface. Compared with monolayer ZrB2–SiC coating (−0.17 mg/s and −8.13 μm/s), the mass and linear variation rates of the laminated coating decreased by 35% and 60%, respectively.

First-principles study on stability, adhesion and fracture properties of ZrO2/W interface in composite materials

Zirconia/tungsten (ZrO2/W) interface is easily formed during the preparation of W-Zr and W-ZrC composites for plasma-facing materials. But there is little information available about the stability, cohesion and bonding of ZrO2/W interface at the atomic scale. Therefore, the thermodynamic stability, mechanical properties and electronic structure of t-ZrO2(001)/W(001) interfaces have been calculated using first-principles calculations. Five kinds of interface bonding structures were considered, and it is found that the two sandwich-like interfaces with one or two stoichimetric ZrO2(001) layers between two W(001) slabs have lower interface energies and better stability than the three precipitate-like interfaces with a ZrO2(001) slab stacked on a W(001) slab, which means that an ultrathin zirconia film tends to form and may promote the grain refinement in W. The analyses of mechanical properties including the work of separation, fracture energy and tensile strengths show that the mechanical failure of the interfaces is inclined to initiate at the interfacial W-O and the O-O bonds, and the ZrO2(001)/W(001) interfaces are less stable against brittle fracture than bulk W and clean W grain boundaries, which implies that the precipitate of ZrO2 particles may act as the crack initiation sites during stretching. Furthermore, the electronic structures analysis indicates that the interfacial W-O bond has some property of covalent and ionic feature. This work could provide a deep understanding of stability, cohesion and fracture properties of ZrO2/W interfaces.

Ablation behaviour of the CVD-(ZrC/SiC)3 alternate coating on C/C composites under oxyacetylene torch with different heat fluxes

The (ZrC/SiC)3 alternate coating prepared on C/C composites by CVD were tested using an oxyacetylene torch with the heat fluxes of 2.38 and 4.18 MW/m2. Results showed that the coating exhibited great ablation resistance under both low and high heat fluxes. Under heat flux of 2.38 MW/m2, the ablation and oxidation occurred layer by layer, while the six layers of coating were reserved after ablation. The SiO2 phase and transitional ZrCxOy layer were formed, providing an effective protection. As the heat flux increased to 4.18 MW/m2, the ablation became more serious while the oxide layer still kept intact on C/C substrate after ablation. Dense and stable layered ZrO2 layers covered on C/C composites after the rapid consumption of SiC layers, which could resist the flame scouring. The (ZrC/SiC)3 alternate coating was demonstrated to have potential in applications under different ablation conditions.

Изучение оптически наведенного заряда наночастиц Au в пленках ZrO-=SUB=-2-=/SUB=-(Y) методом сканирующей Кельвин-зонд микроскопии

Accumulation and relaxation of optically induced electric charge in ZrO2(Y) films with embedded single-layered arrays of Au nanoparticles (NPs) of 2-3 nm in diameter have been studied subject to the depth of the Au NPs in the ZrO2(Y) layers and the optical excitation power at the wavelengths of 473 and 633 nm by Scanning Kelvin Probe Microscopy (SKPM).

Scanning Kelvin Probe Microscopy investigation of optically induced charge in Au nanoparticles embedded into ZrO-=SUB=-2-=/SUB=-(Y) films

Accumulation and relaxation of optically induced electric charge in ZrO2(Y) films with embedded single-layered arrays of Au nanoparticles (NPs) of 2-3 nm in diameter have been studied subject to the depth of the Au NPs in the ZrO2(Y) layers and the optical excitation power at the wavelengths of 473 and 633 nm by Scanning Kelvin Probe Microscopy (SKPM). Keywords: thin film systems, zirconia, nanoparticles, plasmon resonance.

Formation process of zirconia nanotubes and porous structures and model of oxygen bubble growth

Preparation and growth mechanism of anodization of Ti and Al has been widely concerned for two decades, but the research on anodic ZrO2 is relatively lacking. In this paper, anodic TiO2 and ZrO2 nanotubes were prepared in glycerol electrolyte containing 0.35 M NH4F and 4 vol% H2O under different anodizing voltages. We had successfully prepared the anodic ZrO2 nanotubes (AZNTs) with a complete top and a “bulb” at the bottom under 60 V, and with the increase of the applied anodizing voltage, the “bulb” cavity also increased. However, under the same anodizing conditions, the surface of anodic TiO2 nanotubes (ATNTs) is a cluster of nano-tip morphology, and the bottom of the ATNTs is a conventional hemisphere shape. In addition, both AZNTs and porous anodic zirconia (PAZ) were found to coexist in the anodic ZrO2 layer prepared at 60 V. Here, we used the oxygen bubble model and ionic current and electronic current theories to analyze the reason of the special morphology. It is confirmed that the porous anodic oxides are actually evolved from nanotubes. In other words, the structure is essentially the same.

An in situ grown amorphous ZrO2 layer on zeolite for enhanced phosphate adsorption.

Zeolite supported amorphous metal oxide nanolayers with high specific surface area, abundant adsorption sites, and excellent reusability hold a bright prospect in the efficient removal of contaminants, yet it is proven to be still challenging to precisely regulate and control their synthesis. Herein, we reported a facile synthetic strategy for rational design and achieving the uniform and firm in situ growth of an amorphous ZrO2 layer decorated on the surface of zeolite (ZEO@AZ) for enhanced phosphate adsorption. The Langmuir isotherm model and pseudo-second order kinetic equation well described the adsorption process towards phosphate solution, and the synthetized ZEO@AZ exhibited an excellent maximum adsorption amount of 24.98 mgP g−1. Furthermore, the adsorption of phosphates on ZEO@AZ was confirmed to be chemisorption, endothermic and spontaneous. This approach for fabricating amorphous metal oxide nanolayers on a robust matrix may provide a new route for constructing composites with superb phosphate adsorption performance.

Structural and corrosion resistance properties of sputtered zirconium nitride thin films as electrode material for supercapacitor

In this paper, the surface morphology, crystal structure and corrosion resistance of the magnetron sputtered zirconium nitride (ZrN) thin films were evaluated and investigated. The results show that the surface of the prepared films is homogeneous and dense, and the root-mean-square surface roughness (Rq) are 21.0 nm (ZrN0.45), 1.8 nm (ZrN0.4), and 2.0 nm (ZrN0.35), respectively. With the increase of nitrogen partial pressure, the content of Zr3N4 in the ZrN films increased gradually. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements demonstrate that all samples enhance the corrosion performance of ZrN-coated 304 SS. ZrN0.4 possesses a best corrosion resistance in 0.5 M Na2SO4 solution, which maintains complete and dense surface morphologies after 50 h immersion. The underlying related corrosion mechanism was explored and discussed, and the excellent corrosion resistance of ZrN0.4 film on 304 SS can be ascribed to a lower density of pin-hole defects and the dense passive layer of ZrO2.

Amorphous ZrO2 layer conformally grown with zeolite for advanced photocatalytic degradation

Photocatalytic degradation is an efficient approach to handle dyestuff wastewater, but facile synthesis of highly efficient and environmental-friendly photocatalysts is still challenging. Herein, we develop a facile route to fabricate amorphous ZrO2 layers conformally grown with zeolite. The Zeolite@A-ZrO2 exhibits superior photocatalytic performance, outstanding stability and usability towards Rhodamine B dye degradation compared to the pristine Zeolite and A-ZrO2 under simulated sunlight. The superiorities of Zeolite@A-ZrO2 can be attributed to the high specific surface area and favorable stability of Zeolite, the numerous surface defect sites originated from A-ZrO2, and the interfacial interaction resulted in heterojunction, collectively achieving a low recombination rate of electron-hole pairs.

A new kinetic model for CO2 capture on sodium zirconate (Na2ZrO3): An analysis under different flow rates

In this work, it is presented a kinetic study for CO2 capture on Na2ZrO3 as a function of temperature (250−550 °C) and CO2 flow rate (5, 60, and 120 mL/min). We discuss the relevance of a new kinetic model able to fit the experimental data and propose a consecutive reaction model for CO2 capture under low, moderate, and high CO2 flow rates. The proposed model considers that a Na2CO3–ZrO2 layer is formed at the particle surface level, and then, the capture process is later enhanced by Na+ ions diffusion, but its improvement depends entirely on the surface capture. This kinetic approach allowed a better fit for CO2 capture results, describing well the variations obtained as a function of the different flow rates tested between 250 and 550 °C. Thermogravimetric and kinetic data showed that the CO2 capture was benefited as the CO2 flow rate increased from 5 to 120 mL/min. However, high flow rates (60 and 120 mL/min) achieved similar capture efficiencies (Ɛ ≈ 90 %), only once the CO2 sorption-desorption equilibrium was reached. In addition, through the Eyring model analysis, the activated state energy was calculated, being within the range of 0.84 and 1.20 eV for the surface capture and between 0.89 and 1.02 eV for bulk capture (related to Na+ diffusion). In the final section, it was discussed the CO2 sorption-desorption process takes place at both, low temperature and flow rate, and how such a process inhibits or triggers high-temperature CO2 capture.

Hf1–xZrxO2/ZrO2 Nanolaminate Thin Films as a High-κ Dielectric

Engineering of HfO2–ZrO2 ferroelectric thin films can substantially increase their dielectric constant. Here, we investigate dielectric and structural properties of ∼10 nm thin films consisting of stacked 1 nm thin ferroelectric (FE) Hf1–xZrxO2 (HZO(x)) and antiferroelectric (AFE) ZrO2 layers. At x < 0.5, the measurements of polarization vs electric field revealed pure FE hysteresis loops, whereas at x > 0.5, pinched hysteresis loops with some remnant polarization were observed, which indicate a coexistence of FE and AFE orderings. Finally, a pure ZrO2 thin film (x = 1) exhibits only an AFE double hysteresis loop. In this way, we demonstrate that the coexistence of FE and AFE orderings can be controlled by adjusting the composition of HZO(x) layers in the HZO(x)/ZrO2 nanolaminate films. At x = 0.5, the dielectric constant is ∼60 in nanolaminate films, which is much higher than that of the conventional HZO(x) solid solution thin films. Structural investigations confirm a coexistence of polar orthorhombic and nonpolar tetragonal structures, which is consistent with the observed polarization hysteresis loops. We also show that the strain generated in the nanolaminate structure significantly facilitates a field-induced transition from the AFE to the FE phase. The design does not considerably affect the leakage current in HZO(x)/ZrO2 nanolaminate films, which makes this system highly promising for complementary metal oxide semiconductor-compatible capacitors.

Stabilizing Remanent Polarization during Cycling in HZO‐Based Ferroelectric Device by Prolonging Wake‐up Period

AbstractThe stability of remanent polarization (Pr) during multiple operations is critical for memory applications, as the degradation of Pr leads to misreading of stored information. In this letter, improved stabilization of Pr during field cycling in HfZrO4 (HZO)‐based ferroelectric devices by inserting a ZrO2 layer is reported. This optimization method is inspired by the fact that the wake‐up effect of HZO is not obvious. By inserting a ZrO2 layer, which prolongs the wake‐up period, the fatigue process is postponed. Thus, a stabilized Pr is achieved during cycling. The endurance limit can reach over 1010 cycles with no significant decrease in Pr (&lt;5%), which is beneficial for improving the reliability of devices in practical applications.

A Brief Review on the Ferroelectric Fluorite-Structured Nanolaminate

Ferroelectricity can be induced in fluorite-structured oxides such as HfO2 and ZrO2, a feature of increasing interest in both academia and industry. Initially, most research focused on solid solution films, but recently, it has been suggested that nanolaminates with independent HfO2 and ZrO2 layers may show electrical and physical properties superior to those of solid solution samples. It was reported that the nanolaminate samples could have remanent polarization higher than that of solid solution film or a wider composition window for robust ferroelectricity compared to the solid solution films. In this review, the existing literature on fluorite-structured nanolaminates is comprehensively reviewed.

Uncertainty Quantification of the PHEBUS FPT-1 Test Modelling Results

One of the biggest experimental programs helping to improve nuclear installation safety is PHEBUS, an international cooperative research program that provides data for validating computer codes dedicated to the analysis of severe accidents and their calculation results. In the European Union, HORIZON 2020 EURATOM project MUSA (Management and Uncertainties of Severe Accidents) is in progress. Modelling of the PHEBUS FPT-1 test within the frame of this project is provided by project partners using different severe accident codes. Uncertainty quantification of the received results is provided using different methods and statistical tools. The Lithuanian Energy Institute (LEI) is taking part in the MUSA project and this uncertainty exercise. LEI is using the RELAP/SCDAPSIM severe accident code together with GRS methodology and SUSA statistical tool to evaluate the uncertainties of modelling results of PHEBUS FPT-1 test. In this article, uncertainty quantification of the PHEBUS FPT-1 test modelling results provided by LEI in the frame of MUSA project are presented. Provided uncertainty analysis for total hydrogen generation showed that upper and lower uncertainty limits are bounding the experimental data. At the end of the calculation, the upper and lower uncertainty limits of calculations are within the band of experimental uncertainties. Uncertainty analysis for Cs/I release fraction showed that uncertainty limits are bounding experimental data until the middle of the heat-up phase, but at the end of the experiment, the calculated upper uncertainty limit is lower than the experimental data. Results of sensitivity analysis showed that the thermal conductivity of the ZrO2 layer of the shroud has the dominant influence on hydrogen generation and Cs/I release fraction calculation results. Other important parameters are changing at the different experimental phases. In the future, it is planned to update the RELAP/SCDAPSIM model for the PHEBUS FPT-1 test using the results of the provided sensitivity analysis. This will allow a better agreement with experimental data.

Novel one-step formed composite reinforcement of "Spider web like" SiCnw networks and "Z-pins like" SiC rods for ablation resistance improvement of C/C-ZrC-SiC

A novel composite reinforcement with horizontal multilayer "Spider web like" SiC nanowire networks and vertical interconnected "Z-pins like" SiC rods was designed and prepared by facile one-step figuration. The linear ablation rate of "Spider web like" SiC nanowire networks and "Z-pins like" SiC rods collectively reinforced C/C-ZrC-SiC composites at 2610 ± 20 ℃ was 0.4 ± 0.03 μm/s with a 74.19 % reduction. The improved ablation resistance was attributed to a denser gradient oxide layer composed of central ZrO2 layer, transitional ZrO2-SiO2 layer and marginal SiO2 layer generated under the initial sticky net effect from SiCnw networks and subsequent oxide compensation from "Z-pins like" SiC rods.