Zirconia Films Research Articles

Potentiation and depression behaviour in a two-terminal memristor based on nanostructured bilayer ZrO x /Au films

The emulation of synaptic functions such as potentiation and depression is of strategic importance for the development of artificial neuromorphic architectures. Memristors can qualitatively reproduce the short-term plasticity behaviour of biological synapses by exploiting the gradual relaxation of resistance levels upon the removal of the switching signals. Various types of memristors based on nanofabricated metal-oxide-semiconductor stacks have been proposed for this purpose. Here we present a different fabrication approach based on cluster-assembled nanostructured zirconia and gold films (ns-Au/ZrO x ) deposited in a bilayer planar configuration. This device shows memristive behaviour with short-term memory and potentiation/depression. The observed relaxation can be described by a stretched-exponential function. Furthermore, the characteristic time of the short-term phenomena dynamically changes under repeated pulses application. Our nanostructured device is characterised by a substantially larger conductive path length with respect to other nanoscale memristive devices; the use of a zirconia nanostructured film makes the device compatible with neuronal cell culture.

WITHDRAWN: Precession electron diffraction study on the microtexture of the zirconium oxide film in aqueous solutions

The oxide film formed on zirconium alloy (Zr-0.45 Sn-0.38 Nb-0.30 Fe-0.05 Cu-0.015 Si-0.13 O, wt. %) respectively corroded for 300 days in 360 °C/18.6 MPa pure water and lithiated water was characterized using precession electron diffraction (PED). The results revealed that the grain morphology (columnar and equiaxed) and the grain crystallography orientation (angular deviation of {112¯}m-ZrO2 from the oxide growth direction) gradually changed periodically with the distance of metal/oxide (O/M) interface. In lithiated water sample, the proportion of oxide grains deviated from the {112¯}m-ZrO2 texture by 50-60° is higher than that in pure water, resulting in an early corrosion transition. This is attributed to that Li+ ions were unfavorable for the formation of well-oriented and coarse columnar grains. In the pure water, a small amount of hexagonal ZrO (h-ZrO) suboxide was found at the O/M interface where just go trough a high-rate corrosion transition, while in the lithiated water, a continuous h-ZrO suboxide layer was formed at the O/M interface where experiences a low-rate corrosion just before transition. This suggests that the present of suboxide layer greatly correlates to the instantaneous oxidation rate. Electron energy loss spectroscopy (EELS) further found that the presence of h-ZrO affected the oxygen level in the nearby substrate metal.

Electron-beam synthesis of ceramic- and boron-based coatings

We report the results of our experimental investigations on the synthesis of coatings based on various ceramics and boron. The coatings were synthesized by electron-beam evaporation of solid dielectric targets of Al2O3, YSZ, Al2O3Cr, and B. The deposition rates for coatings based on these materials were measured. The deposition rate of defect-free coatings was 1200–1600 nm min−1. The obtained coatings, up to 5 μm thick, were studied in terms of their morphology, structure, and tribological properties. The coatings are uniform in thickness, composition and free of impurities. The coatings, with the exception of the zirconium oxide film, have a predominantly amorphous structure. Comparisons of their mechanical and tribological characteristics are presented. The hardness of the coatings formed from YSZ was 0.4 GPa, from aluminum oxide ceramics 4–6 GPa, and from boron 11 GPa. Boron-based coatings were found to be the most wear-resistant (with wear coefficient about 8.9·10−6 mm3 N−1·m−1).

Fabrication of sub-5 nm uniform zirconium oxide films on corrugated copper substrates by a scalable polymer brush assisted deposition method

We demonstrate a polymer brush assisted approach for the fabrication of continuous zirconium oxide (ZrO2) films over large areas with high uniformity (pin-hole free) on copper (Cu) substrates. This approach involves the use of a thiol-terminated polymethyl methacrylate brush (PMMA-SH) as the template layer for the selective infiltration of zirconium oxynitrate (ZrN2O7). The preparation of a highly uniform covalently grafted polymer monolayer on the Cu substrate is the critical factor in fabricating a metal oxide film of uniform thickness across the surface. Infiltration is reliant on the chemical interactions between the polymer functional group and the metal precursor. A following reductive H2 plasma treatment process results in ZrO2 film formation whilst the surface Cu2O passive oxide layer was reduced to a Cu/Cu2O interface. Fundamental analysis of the infiltration process and the resulting ZrO2 film was determined by XPS, and GA-FTIR. Results derived from these techniques confirm the inclusion of the ZrN2O7 into the polymer films. Cross-sectional transmission electron microscopy and energy dispersive X-ray mapping analysis corroborate the formation of ZrO2 layer at Cu substrate. We believe that this quick and facile methodology to prepare ZrO2 films is potentially scalable to other high-κ dielectric materials of high interest in microelectronic applications.

Solution processed rare-earth doped high-k dielectrics for low-power IGZO transistors

Low-power metal oxide transistors are highly required in displays, logic circuit and sensors. High quality gate dielectrics with the properties of high dielectric constant, smooth surface, and excellent insulating performance are critical to realize the above mentioned transistors. In this work, we present a universal strategy by using rare-earth (RE) elements (Y, Er and Yb) as dopants to improve the dielectric properties of zirconia film for low-power transistors. Additionally, all the dielectric films are prepared by solution process, which is compatible with low-cost and large-area manufacturing technology. The leakage current densities of zirconia films decrease from 1.27 × 10−5 A/cm2 to 2.8 × 10−7 A/cm2, 6.6 × 10 − 7 A/cm2, and 4.3 × 10−7 A/cm2 by doping a small amount of Y, Er, and Yb in zirconia films, respectively. Furthermore, bottom-gate top-contact indium-gallium-zinc oxide (IGZO) transistors with RE-doped zirconia dielectrics show one order improved current on/off (∼104) ratio and achieve one order improvement in mobility (3.11, 2.85, 2.75 cm2V−1S−1 for Y-, Er-, Yb-doped devices respectively) compared with that of pure zirconia film based devices (0.30 cm2V−1S−1). Moreover, the subthreshold swing (SS) of TFTs based on RE-doped and undoped ZrO2 dielectric films are calculated (0.2, 0.36, 0.21 V/dec for Y-, Er-, Yb-doped devices respectively, and 0.51 V/dec for undoped devices) This study demonstrates the validity of RE ions as dopants in gate dielectrics to achieve high-performance low-power metal oxide transistors.

Effect of calcination temperature on sensing performance of YSZ based electrochemical H2S gas sensor with a NiFe2O4 electrode

Electrochemical gas sensors based on yttria-stabilized zirconia (YSZ) film have attracted ascending attention for detecting H2S. Due to the poor sinterability of YSZ film, high-temperature calcination is usually required in the preparation procedure to ensure the good contact between YSZ and sensing electrode, which could particularly limit the triple phase boundary (TPB) length at the interface of H2S|YSZ|sensing electrode as well as the porosity of sensing electrode. Therefore, the calcination temperature would significantly affect the sensing performance, which has been ignored in reported studies. In this work, YSZ based electrochemical gas sensors with NiFe2O4 (NFO) sensing electrode are prepared to detect H2S at ppb-level. The effect of the calcination temperature of NFO sensing electrode on the sensing performance is investigated. The sensor with an optimal calcination temperature of 1000 °C delivers a response value of − 42 mV for 500 ppb H2S at 460 °C with a detection limitation of 10 ppb H2S. Good linear slopes with a sensitivity of − 13.1 mV/decade toward 20–100 ppb H2S and a sensitivity of − 46.9 mV/decade toward 100–500 ppb H2S are obtained. Meanwhile, the sensor also displays attracting stability and short response/recovery time. The good sensing performance is attributed to enhanced TPB length, good porosity of NFO electrode and limited interaction between the NFO and YSZ film by optimizing the calcination temperature of NFO sensing electrode.

Effect of Heat Treatment on Zirconium Oxide High‐k Gate Dielectric in Silicon‐Based Metal Oxide Semiconductor Capacitors

Herein, zirconia thin films are successfully prepared on silicon substrates using the sol–gel method, and the microstructure, optical, and electrical properties of zirconia high‐k gate dielectric films are analyzed at different annealing temperatures. X‐ray diffraction results show that ZrO2 films crystallize above 500 °C and the grain size increases with the increase of annealing temperature; X‐ray photoelectron spectroscopy analysis confirms that metal–oxygen bonds can be effectively formed and defects in the films are eliminated by annealing treatment, with significant changes in the valence band shift (ΔEv) and conduction band shift (ΔEc) with increasing annealing temperature. Analysis of the optical properties of the films by UV‐Vis confirms that all zirconia films have high transmittance, with the bandgap increasing from 5.54 to 5.74 eV with increasing annealing temperature. Atomic force microscope and field emission scanning electron microscope show that the film quality is better and the root mean square roughness of the zirconia films increases from 0.551 to 1.190 nm and the film thickness decreases from 176.19 to 58.73 nm with increasing annealing temperature. Electrical performance tests show that proper annealing is effective in improving electrical properties, such as obtaining a larger dielectric constant (k) and a lower leakage current density.

Ultra-thin ZrO2 overcoating on CuO-ZnO-Al2O3 catalyst by atomic layer deposition for improved catalytic performance of CO2 hydrogenation to dimethyl ether

An ultra-thin overcoating of zirconium oxide (ZrO2) film on CuO-ZnO-Al2O3 (CZA) catalysts by atomic layer deposition (ALD) was proved to enhance the catalytic performance of CZA/HZSM-5 (H form of Zeolite Socony Mobil-5) bifunctional catalysts for hydrogenation of CO2 to dimethyl ether (DME). Under optimal reaction conditions (i.e. 240 °C and 2.8 MPa), the yield of product DME increased from 17.22% for the bare CZA/HZSM-5 catalysts, to 18.40% for the CZA catalyst after 5 cycles of ZrO2 ALD with HZSM-5 catalyst. All the catalysts modified by ZrO2 ALD displayed significantly improved catalytic stability of hydrogenation of CO2 to DME reaction, compared to that of CZA/HZSM-5 bifunctional catalysts. The loss of DME yield in 100 h of reaction was greatly mitigated from 6.20% (loss of absolute value) to 3.01% for the CZA catalyst with 20 cycles of ZrO2 ALD overcoating. Characterizations including hydrogen temperature programmed reduction, x-ray powder diffraction, and x-ray photoelectron spectroscopy revealed that there was strong interaction between Cu active centers and ZrO2.

Optical characterization of the impact of 100 keV protons on the optical properties of ZrO2 films prepared by ALD on fused silica substrates.

Atomic layer deposition (ALD)-grown zirconia films underwent irradiation by 100keV protons at fluences ranging from 1⋅1012 p +/c m 2 through 5⋅1014 p +/c m 2. The induced structural damage was modeled using the stopping and range of ions in matter (SRIM) and compared with the change of the optical properties characterized by ellipsometry, spectrophotometry, and x-ray reflectometry. Proton-induced contamination of the optical surface due to deposition of a carbon-rich layer was determined. Correct estimation of the substrate damage was shown to be critical for reliable evaluation of the optical constants of the irradiated films. The ellipsometric angle Δ is shown to be sensitive to both the presence of the buried damaged zone in the irradiated substrate and the contamination layer on the surface of the samples. The complex chemistry in carbon-doped zirconia accommodating over-stoichiometric oxygen is discussed, along with the impact of the film composition change on the refractive index of the irradiated films.

Temperature-switched orientation properties through physicochemically constructed aluminum zirconium oxide films

In general, it has one of the characteristics of homeotropic alignment and homogeneous alignment depending on the material and manufacturing process of the liquid crystal alignment layer. However, in this study, we propose a new type of alignment film that has the characteristics of changing the liquid crystal alignment direction according to the curing temperature. The AlZrO alignment film produced by the solution process and brush coating method showed homeotropic alignment characteristics when cured at low temperatures and homogeneous alignment characteristics when cured at high temperatures. These switching characteristics according to the curing temperature showed stable LC alignment, respectively, and the threshold voltages were 0.81 V and 0.857 V in vertical alignment (VA) mode and twisted nematic (TN) mode, respectively, demonstrating excellent electro-optical properties. The mechanism of these switching characteristics was analyzed through surface modification analysis. This study introduces new insights into liquid crystal alignment films that satisfy all of the high-efficiency fabrication process, various application possibilities due to their switching properties, and excellent electro-optical properties.

Epitaxial growth of high-quality yttria-stabilized zirconia films with uniform thickness on silicon by the combination of PLD and RF sputtering

High-quality (100)-oriented yttria-stabilized zirconia (YSZ) films with uniform thickness were epitaxially grown on silicon substrates by a two-step process of pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (RFS). First, we fabricated a YSZ-seed layer on (001)-oriented silicon substrates using a PLD apparatus, and then transferred the YSZ-seed substrate to an RFS equipment to complete the growth of a thicker YSZ film. The dependence of YSZ crystal quality on RFS-growth temperature was investigated in the range of 200 to 850 °C. All the resulting YSZ films exhibited pure (100) orientation, and the full width at half maximum of the YSZ (200) X-ray rocking curve was as low as 0.64° for the YSZ film grown at 850 °C, and increased to 1.02° with the RFS-growth temperature declining to 200 °C. The results evidenced that the YSZ film can be epitaxially grown at 200 °C in the presence of a YSZ-seed layer. However, the splitting of the YSZ (200) X-ray diffraction peak appeared at 500 °C and 200 °C, which may be attributed to a transformation of the intrinsic stress in the YSZ films from compressive to tensile stress with decreasing temperature. In addition, the YSZ film had a uniform thickness distribution with an inhomogeneity of less than 5 % and a very flat and dense surface with root-mean-square surface roughness below 1 nm.

Zr-Ti getter film integration in MEMS vacuum packaging

Titanium, zirconium, and Zr-Ti alloy thin films were evaporated under UHV. AFM, TEM and SEM observations showed that grain size at the surface of the films varies with their thickness and composition. The single-metal films exhibit larger grain than alloy films. The highest density of grain boundaries is found for Zr-Ti film with a balanced content in Zr and Ti. For the three types of films, the grain boundary density at the surface decreases when increasing the film thickness. The gettering properties of the films were studied by activation annealing in the range of 200 °C–400 °C by in situ sheet resistance monitoring and by integrating them into MEMS packages sealed at 300 °C. In both cases, the sorption of gases was found to increase with the surface density of grain boundaries. In the specific activation conditions of MEMS packaging, it is shown that reducing the film thickness from 400 nm to 50 nm enhances gas sorption by the Zr-Ti getter and for the first time, the activation of a getter film thinner than 100 nm integrated in a MEMS package was demonstrated.

Chemical states of PVD-ZrS2 film underneath scaled high-k film with self-oxidized ZrO2 film as interfacial layer

Zirconium disulfide (ZrS2)—an attractive next-generation channel material because of its high mobility—is stabilized in the air by a zirconium dioxide (ZrO2) film which functions as a high-k film in MISFET. We fabricated high-k/PVD-ZrS2 stacks with a self-oxidized ZrO2 film as an interfacial layer; their chemical properties were analyzed to clarify how each fabrication process affects the ZrS2 under the oxide film. The results clarified that sulfur vapor annealing (SVA) is critical for fabricating high-quality physical vapor deposition (PVD) ZrS2 films and that the change in surface potential of the ZrS2 films due to interface dipoles between the high-k and Zr-compound films is suppressed with scaling of high-k thickness. The SVA with high-k films also prevents degradation of crystallinity and stoichiometry, enhancing the quality of the ZrS2 films without affecting their surface potential. These achievements enable us to control the threshold voltage in ZrS2 MISFETs.

Flexible piezoelectric nanocomposites based on PVDF-HFP/PLA blend doped PZT

In the present work, we studied the effect of adding PZT nanoparticles to PVDF-HFP/PLA matrix on piezoelectric properties of blend-based nanocomposites. Polyvinylidene fluoride hexafluoro-propylene /Polylactic acid /Lead titanate zirconate (PVdF-HFP/PLA/PZT) films nanocomposites were prepared by solvent casting technique using different percentages of PZT Nano fillers. The different samples were characterized by Polarized optical microscope (POM), Fourier transformed infrared (FTIR) and Thermogravimetric analysis (TGA).POM images indicate uniform distribution of PZT Nano fillers in the PVdF-HFP/PLA matrix. FTIR analysis reveals the appearance of β-phase in nanocomposites and the enhancement of their piezoelectric properties. These electroactive nanocomposites thin films are a potential candidate for the piezoelectric Nano generators, energy storage devices and energy harvesting applications.

Cubic phase optimization and influence of post-annealing on microstructure, optical, wetting, and nanomechanical properties of zirconia thin films

This work reports the fabrication of zirconia thin films by e-beam deposition, followed by thermal annealing in air at different temperatures to optimize the cubic phase without using any dopants or chemical stabiliser. The X-ray diffraction (XRD) and Raman spectra of zirconia films annealed at 500 °C reveal the formation of stable cubic phase with a crystallite size of 10.7 ± 0.8 nm at room temperature. Optical transparency of the zirconia film annealed at 500 °C is high, approaching 80% in the visible range. Increasing annealing temperature improves crystallinity, hydrophilicity and reduces nonradiative associated defects. The mechanical properties of zirconia films examined using static and dynamic nanoindentation demonstrate that hardness increases from 7.60 ± 0.26 GPa to 11.08 ± 0.90 GPa and elastic modulus increases from 170.74 ± 4.98 GPa to 210.13 ± 5.56 GPa when annealing temperature increases. The post-annealing temperature influences provide a method for tuning the optical, wetting and mechanical characteristics of zirconia thin film.

Synthesis of crystalline BaZrO3 thin films over preferred-oriented ZrN by a hydrothermal-galvanic couple method for photoelectrochemical evaluations

Crystalline barium zirconate (BaZrO 3 ; BZO) films which could be applied to photoelectrochemical cells and fuel cells were synthesized by a hydrothermal-galvanic couple (HT–GC) method using preferred-oriented ZrN thin-film electrodes. The HT–GC synthesis was carried out at 90°C in alkaline solutions. Substantial galvanic currents were detected without applying any external power sources throughout the synthesis. X-ray diffraction patterns reveal that BZO films with different crystallinities were achieved by such a facile synthesis. Moreover, the BZO films that grew on close-packed (200)-preferred oriented ZrN underlayer exhibited higher crystallinity and growth rates than on the (111)-preferred oriented ZrN. The obtained BZO films exhibited fast on-off photoelectrochemical responses while the BZO films with higher crystallinity over the (200)-ZrN possessed better photoelectrochemical responses. • Crystalline BaZrO3 films could be synthesized on ZrN by a hydrothermal-galvanic couple method • Crystallinity and photoelectrochemical performance of the films were tailored through ZrN • Galvanic effects were enhanced by using (200)-oriented ZrN rather than (111) oriented ZrN • Higher crystallinity of the films could be achieved by a more close-packed (200)-ZrN • Better and fast on-off photoelectrochemical responses of the films were obtained by (200)-ZrN

Polyether Ether Ketone Coated with Ultra-Thin Films of Titanium Oxide and Zirconium Oxide Fabricated by DC Magnetron Sputtering for Biomedical Application.

Recently, polyether ether ketone has raised increasing interest in research and industry as an alternative material for bone implants. This polymer also has some shortcomings, as it is bioinert and its surface is relatively hydrophobic, causing poor cell adhesion and therefore slow integration with bone tissue. In order to improve biocompatibility, the surface of polyether ether ketone-based implants should be modified. Therefore, polished disc-shaped polyether ether ketone samples were surface-modified by direct current magnetron sputtering with ultrathin titanium and zirconium coatings (thickness < 100 nm). The investigation results show a uniform distribution of both types of coatings on the sample surfaces, where the coatings mostly consist of titanium dioxide and zirconium dioxide. Differential scanning calorimetry revealed that the crystalline structure of the polyether ether ketone substrates was not changed by the coating deposition. Both coatings are amorphous, as shown by X-ray diffraction investigations. The roughness of both coating types increases with increasing coating thickness, which is beneficial for cell colonization. The coatings presented and investigated in this study improve wettability, increasing surface energies, in particular the polar component of the surface energies, which, in turn, are important for cell adhesion.

Antibacterial effect of surface-modified Zr50Cu50 metallic glass

Zr-based metallic glasses generally have an amorphous zirconium oxide film that strongly inhibits further oxidation. However, surface defects may deteriorate the glass stability of the amorphous oxide film, leading to the formation of a thick natural oxide layer. In this study, we demonstrated that the change in the oxidation behavior of a melt-spun Zr50Cu50 metallic glass foil caused by the surface casting defects on its wheel side can lead to a dramatic improvement in antibacterial properties. The superior antibacterial properties of the wheel side was attributed to the metallic Cu islands exposed on the surface.

Applications and Advantages of Atomic Layer Deposition for Lithium-Ion Batteries Cathodes: Review

Nowadays, lithium-ion batteries (LIBs) are one of the most convenient, reliable, and promising power sources for portable electronics, power tools, hybrid and electric vehicles. The characteristics of the positive electrode (cathode active material, CAM) significantly contribute to the battery’s functional properties. Applying various functional coatings is one of the productive ways to improve the work characteristics of lithium-ion batteries. Nowadays, there are many methods for depositing thin films on a material’s surface; among them, one of the most promising is atomic layer deposition (ALD). ALD allows for the formation of thin and uniform coatings on surfaces with complex geometric forms, including porous structures. This review is devoted to applying the ALD method in obtaining thin functional coatings for cathode materials and includes an overview of more than 100 publications. The most thoroughly investigated surface modifications are lithium cobalt oxide (LCO), lithium manganese spinel (LMO), lithium nickel-cobalt-manganese oxides (NCM), lithium-nickel-manganese spinel (LNMO), and lithium-manganese rich (LMR) cathode materials. The most studied processes of deposition are aluminum oxide (Al2O3), titanium dioxide (TiO2) and zirconium dioxide (ZrO2) films. The primary purposes of such studies are to find the synthesis parameters of films, to find the optimal coating thickness (e.g., ~1–2 nm for Al2O3, ~1 nm for ZrO2, <1 nm for TiO2, etc.), and to reveal the effect of the coating on the electrochemical parameters of batteries. The review summarizes synthesis conditions, investigation results of deposited films on CAMs and positive electrodes and some functional effects observed due to films obtained by ALD on cathodes.

(Invited) Advances in Atomic Layer Processing of Hafnia-Zirconia Ferroelectrics

The limits of integrating ferroelectric materials on commercial semiconductor chips were demolished the moment ferroelectricity in hafnia and zirconia films was reported in 2011. This breakthrough moment in the history of ferroelectric materials was made possible by the fortuitous interplay between advances in atomic layer processing and the strong surface energy dependence of crystal phases in HfO2 and ZrO2. Aided by commercial investment in using both materials as high-k gate and DRAM dielectric materials, atomic layer deposition (ALD) processes are beginning to take full advantage of the completely solid-soluble hafnia-zirconia (Hf1-xZrxO2) ferroelectric system with new precursors and new insights obtained by systematically evaluating film growth conditions. The capability to precisely adjust the compositional profile and to alter oxidation conditions during atomic layer deposition film growth are giving an unprecedented level of control to engineer Hf1-xZrxO2 and doped HfO2 thin films for ferroelectric applications.The latest advances in atomic layer processing of Hf1-xZrxO2 and doped-HfO2 are presented where the dynamic interaction between composition and film growth conditions provide an engineering roadmap to adjust the physical and structural properties of the dielectric films. Metal precursors play a crucial role in the ensuing film properties. The adjustability of the electrical and structural properties of Hf1-xZrxO2 with ozone exposure during ALD film growth is discussed with respect to the important role oxygen and oxygen vacancies have in the overall phase stability of these novel ferroelectric materials, as well as C incorporation caused by ALD precursors. Just as atomic layer deposition has proven to be instrumental in the discovery and stabilization of the ferroelectric phase in HfO2-based thin films, atomic layer etching (ALE) of HfO2/ZrO2-based layers is now being used to preserve ferroelectricity while pushing the thickness dimension to new limits, yielding high performance films for ferroelectric tunnel junction applications. Further innovations in atomic layer processing will continue to be a harbinger of high performance ferroelectrics in the coming years based on the current status and future outlook for ferroelectric Hf1-xZrxO2 and other emerging ferroelectric materials.