ZrO2 Thin Films Research Articles

Exploring the impact of thin film thicknesses on the linear and nonlinear optical properties of ZrO2 thin film

Exploring the impact of thin film thicknesses on the linear and nonlinear optical properties of ZrO2 thin film

Investigation of Structural, Mechanical, Tribological and Wettability Properties of ZrO2 Thin Films Grown by DC Magnetron Sputtering Method

To improve the mechanical and tribological properties of biomedical materials, biocompatible coatings are obtained on surfaces using various methods. In this study, ZrO2 thin films were deposited on CP-Ti material used as biomaterial by DC magnetron sputtering method. In this context, structural, mechanical, tribological and wettability properties of ZrO2 film coated on CP-Ti base material were investigated. X-ray diffraction method (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to characterize the crystallographic structure and surface morphology of the obtained film. Microhardness and wear tests were carried out to investigate the mechanical and tribological properties of the coatings. Additionally, contact angle measurements were made with pure water and ethylene glycol to determine the hydrophobicity and oleophobicity properties of the ZrO2 coated samples. The water contact angle and the oil contact angle of the film are 105.4° and 73.2, respectively. The results showed that ZrO2 coating film deposited on surfaces by DC magnetron sputtering method was more resistant to wear compared to bare CP-Ti.

Optimization of molar concentrations for enhanced crystallinity and bandgap tuning of ZrO2 thin films via spray pyrolysis for advanced optical applications

In this study, Zirconium oxide (ZrO2) thin films were synthesized on glass substrates at 400°C using the Spray Pyrolysis method, due to its simplicity, cost-effectiveness, and precise control. The films were prepared at varying molar concentrations (0.1, 0.15, and 0.2 M) and analyzed for their structural, optical, and morphological properties. X-ray diffraction (XRD) confirmed that all films exhibited a tetragonal crystalline structure with a preferred orientation along the (101) plane. The crystallite size, calculated using the Scherrer equation, reached a maximum of 27.26 nm at 0.2 M concentration, indicating improved crystallinity with higher concentration. Optical studies revealed a decrease in transmittance and an increase in absorbance in the visible region as the concentration increased, accompanied by a reduction in the optical band gap from 3.84 to 3.57 eV and an increase in Urbach energy. Scanning Electron Microscopy (SEM) images showed that the films had a dense and smooth morphology, while Energy Dispersive X-ray (EDX) analysis confirmed the elemental presence of zirconium and oxygen in the films.

A new way to tune photocatalytic activity, surface morphology, and structural/optical parameters of ZrO2 thin films using different Zr sources along with annealing temperature and film thickness

A new way to tune photocatalytic activity, surface morphology, and structural/optical parameters of ZrO2 thin films using different Zr sources along with annealing temperature and film thickness

Comparative analysis of structural characteristics and thermal insulation properties of ZrO2 thin films deposited via chemical and physical vapor phase processes

ZrO2 is a flagship material for the development of efficient thermal barrier coatings not only for aerospace applications but also on steel molds for plastic injection, especially to produce high quality miniaturized parts of low environmental impacts. In the present study, ZrO2 thin films of thicknesses ranging between 4 and 40 μm were deposited on steel substrates by two key gas phase technologies, magnetron sputtering (PVD) and direct liquid injection metal organic CVD (DLI-MOCVD). The film morphology, structure and chemical composition were comparatively investigated and correlated to their heat transfer properties. All films were nearly stoichiometric and presented a columnar structure mainly formed of the monoclinic crystalline phase. The magnetron sputtering coatings were denser and smoother than the CVD ones, for which highly porous tree-like microstructures were observed without degradation of their mechanical properties. All films exhibited efficient thermal insulation properties, the thickest 40 µm magnetron sputtering coating displaying the most significant reduction in heat transfer. The CVD films provided the highest thermal gradient decrease across their thickness, probably thanks to their higher porosity associated to a multi-angle tree-like columnar structure, both acting as scattering zones of phonons involved in heat flow diffusion. By controlling the local deposition conditions influencing the nucleation and growth mechanisms, the film porous microstructure can thus be tuned to optimize the coating thermal properties.

Remote vapor-phase dual alkali halide salts assisted quasi-van der Waals epitaxy of m-phase ZrO2 thin films with high dielectric constant and stable flexible properties

High-κ dielectric constant and wideband gap of ZrO2 material render it as an excellent candidate for transistor gate dielectric layers. However, current reported synthesis techniques suffer the problems of high precursor volatilization rate, ultrasmall grains with low dielectric constant, and high leakage current, which largely impede its application in electronic devices. Here, the quasi-van der Waals epitaxy growth of compact m-phase ZrO2 thin films has been developed, in which the stable supply of Zr source is realized by the tuned sublimation of ZrC powder with remote vapor-phase dual halide salts assistant. The formation of m-phase ZrO2 is due to the lower Gibbs free energy, in which the crystal nucleates at the etched hole edges of mica substrate, thus forming hexagonal shape polycrystal grains and merging as the continuous thin films. The microstructures and Raman spectrum characterization reveal the two dominated growth orientations and good crystal qualities, which indicate the uniform dielectric constant. The excellent growth reproducibility could be easily adapted to thin metal substrates, such as tungsten, molybdenum, and stainless steel, where the adhesion strength is strong because of the higher density of interfacial chemical bonding. Meanwhile, the metal–insulator–metal flexible capacitors show the high dielectric constant of 23–26 and low leakage current density of 10−4 A/cm2 at large voltage and only exhibit the decreased capacitance density of 7% after several hundred bending cycles. Our work paves a way to achieve the high-quality dielectric thin films on various substrates by the unique chemical vapor deposition design strategy.

Enhanced polarization and endurance properties of ZrO2-based ferroelectric capacitor using HfO2 interfacial layer

Recently discovered ferroelectricity in fluorite-structure ZrO2 thin film has attracted increasing and intense interest due to its lower crystallization temperature and higher content in nature in comparison to hafnium oxide. Here, the effect of HfO2 interfacial layer on the ferroelectric properties of ZrO2 thin films is investigated systematically by designing four types of interfacial structures. It is revealed that the ferroelectric orthorhombic phase, remanent polarization, and endurance can be improved in ZrO2 thin film by inserting both a top- and bottom-HfO2 interfacial layer. A maximal ferroelectric remanent polarization (2P r) of 53.4 μC cm−2 and an optimal endurance performance of 3 × 107 field cycles under frequency of 100 kHz are achieved in Pt/HfO2/ZrO2/HfO2/Pt capacitors, with ferroelectric stacks being crystallized at 450 °C via post-deposition annealing method. X-ray photoelectron spectroscopy analysis confirms that the HfO2 bottom-layer plays a very important role in the formation of a higher ratio o-phase, thus enhancing the ferroelectricity. These results suggest that designing appropriate interfaces would help achieve excellent ferroelectric properties in ZrO2 films.

Novel deuterated cyclopentadienyl zirconium/hafnium precursors for atomic layer deposition of high-performance ZrO2/HfO2 thin films

The need to improve the electrical properties of ZrO2 and HfO2 thin films deposited by atomic layer deposition (ALD), which is widely used in the field of microelectronics, is growing. Attempts to improve precursor stability unavoidably lead to reduced reactivity and diminished utility. Therefore, we synthesized and developed two new ALD precursors by introducing deuterium, which simultaneously exhibit enhanced thermal stability and enhanced reactivity as a result of the introduction of deuterium. For the substitution of deuterium for hydrogen in the precursors responsible for the enhanced thermal stability, we experimentally and theoretically demonstrated that thermal stability and reactivity can be simultaneously enhanced by reducing the bonding dissociation energy of ligands that have not undergone deuterium substitution. This observation led to the development of ZrO2 and HfO2 ALD processes that result in no impurities within the thin films and minimal substrate damage even at a very high deposition temperature of 400 °C. In particular, the improvement in crystallinity through ultra-high-temperature ALD deposition resulted in excellent electrical properties in a metal–insulator–metal capacitor in which the film was incorporated; the capacitor demonstrated a dielectric constant of 37.9 and leakage current of 3.52 × 10−9 A cm−2, without the need for a subsequent annealing process.

Electrical Conduction Mechanism of Mg-Doped ZrO2 Thin Films.

Amorphous ZrO2 thin films with increasing Mg content were deposited on quartz substrates, by dip coating method. The films are transparent in the visible domain and absorbent in UV, with an optical band gap that decreases with the increase of Mg content, from 5.42 eV to 4.12 eV. The temperature dependent conductivity measurements showed typical semiconductor comportment. The decrease of the electrical conductivity by Mg doping was related to the increase of the OH groups (37% to 63%) as seen from X-ray Photoelectron Spectroscopy. It was found out that the electrical conductivity obeys the Meyer-Neldel rule. This rule, previously reported for different disordered material systems is obtained for ZrO2 for the first time in the literature. Exploring novel aspects of Mg-doped ZrO2, the present study underscores the origin of the Meyer-Neldel rule explained by the small-polaron hopping model in the non-adiabatic hopping regime. Determination of the presence of such a conduction mechanism in the samples hold promise for comprehending the important aspects, which might be a concern in developing various devices based on Mg-doped ZrO2.

Enhanced Deposition Selectivity of High-k Dielectrics by Vapor Dosing and Selective Removal of Phosphonic Acid Inhibitors.

Area-selective atomic layer deposition (AS-ALD), which provides a bottom-up nanofabrication method with atomic-scale precision, has attracted a great deal of attention as a means to alleviate the problems associated with conventional top-down patterning. In this study, we report a methodology for achieving selective deposition of high-k dielectrics by surface modification through vapor-phase functionalization of octadecylphosphonic acid (ODPA) inhibitor molecules accompanied by post-surface treatment. A comparative evaluation of deposition selectivity of ZrO2 thin films deposited with the O2 and O3 reactants was performed on SiO2, TiN, and W substrates, and we confirmed that high enough deposition selectivity over 10 nm can be achieved even after 200 cycles of ALD with the O2 reactant. Subsequently, the electrical properties of ZrO2 films deposited with O2 and O3 reactants were investigated with and without post-deposition treatment. We successfully demonstrated that high-quality ZrO2 thin films with high dielectric constants and stable antiferroelectric properties can be produced by subjecting the films to ozone, which can eliminate carbon impurities within the films. We believe that this work provides a new strategy to achieve highly selective deposition for AS-ALD of dielectric on dielectric (DoD) applications toward upcoming bottom-up nanofabrication.

Internal strain identification of seed-layered ZrO2, aluminum-, and yttrium-doped ZrO2 thin films via grazing incidence x-ray diffraction

Grazing incidence x-ray diffraction reveals that conventional post-deposition-annealed ZrO2 and in situ crystallized (by local epitaxy) ZrO2 thin films (<15 nm) have different internal strain states. A comparison between single- and two-step grown films enables the diverse strain components to be discretely identified. In particular, thickness-dependent intrinsic growth strain is unevenly distributed within the film according to the Volmer–Weber growth. Furthermore, extrinsic thermal strain, locally present in the annealed seed layer, does not spread over the in situ crystallized upper main layer of the two-step film. Post-deposition annealing of the two-step film renders the strain state identical to the single-step films by imposing thermal strain on the in situ crystallized main layer. Local strains created by diffused aluminum and yttrium dopants are also examined. Since each stress factor plays a vital role in the phase formation and electrical behaviors of ZrO2 and other fluorite-structure films, this method will pave the way for understanding the film's internal strain distribution and accompanying performance engineering.

Comparative performance of fluorite-structured materials for nanosupercapacitor applications

Over the last fifteen years, ferroelectric (FE) and antiferroelectric (AFE) ultra-thin films based on fluorite-structured materials have drawn significant attention for a wide variety of applications requiring high integration density. AFE ZrO2, in particular, holds significant promise for nanosupercapacitors, owing to its potential for high energy storage density (ESD) and high efficiency (η). This work assesses the potential of high-performance Hf1−xZrxO2 thin films encapsulated by TiN electrodes that show linear dielectric (LD), FE, and AFE behavior. A wake-up effect is observed for AFE ZrO2, a phenomenon barely reported for pure zirconium oxide and AFE materials in general, correlated with the disappearance of the pinched hysteresis loop commonly observed for Zr-doped HfO2 thin films. ESD and η are compared for FE, AFE, and LD samples at the same electrical field (3.5 MV/cm). As expected, ESD is higher for the FE sample (95 J/cm3), but η is ridiculously small (≈55%) because of the opening of the FE hysteresis curve, inducing high loss. Conversely, LD samples exhibit the highest efficiency (nearly 100%), at the expense of a lower ESD. AFE ZrO2 thin film strikes a balance between FE and LD behavior, showing reduced losses compared to the FE sample but an ESD as high as 52 J/cm3 at 3.5 MV/cm. This value can be further increased up to 84 J/cm3 at a higher electrical field (4.0 MV/cm), with an η of 75%, among the highest values reported for fluorite-structured materials, offering promising perspectives for future optimization.

Influence of Biaxial Strain and Interfacial Layer Growth on Ferroelectric Wake-Up and Phase Transition Fields in ZrO2.

Investigations on fluorite-structured ferroelectric HfO2/ZrO2 thin films are aiming to achieve high-performance films required for memory and computing technologies. These films exhibit excellent scalability and compatibility with the complementary metal-oxide semiconductor process used by semiconductor foundries, but stabilizing ferroelectric properties with a low operation voltage in the as-fabricated state of these films is a critical component for technology advancement. After removing the influence of interfacial layers, a linear correlation is observed between the biaxial strain and the electric field for transforming the nonferroelectric tetragonal to the ferroelectric orthorhombic phase in ZrO2 thin films. This observation is supported by applying the principle of energy conservation in combination with ab initio and molecular dynamics simulations. According to the simulations, a rarely reported Pnm21 orthorhombic phase may be stabilized by tuning biaxial strain in the ZrO2 films. This study demonstrates the significant influence of interfacial layers and biaxial strain on the phase transition fields and shows how strain engineering can be used to improve ferroelectric wake-up in ZrO2.

High stability and photocatalytic activity of N-doped ZrO2 thin films

Undoped and nitrogen-doped ZrO2 thin films were obtained by HiPIMS on ITO/glass substrates. To stabilize their structure, the films were subjected to a heat treatment. The properties of the heat-treated films (structure, morphology, elemental composition of the atomic species at the films surface, optical band gap, wettability and oxidation performance of Rhodamine B) were correlated. Some properties of the studied films were compared with the ones of the as-deposited films previously reported. By nitrogen doping, zirconia thin film modifies its fundamental absorption edge, becoming absorbent in the visible domain. The heat treatment improves the hydrophilic properties of both undoped and N-doped films, the last one becoming super-hydrophilic. The photocatalytic activity under UV was investigated for three RhB concentrations. The degradation efficiency is higher than 90 % for both undoped and N-doped ZrO2 films, being better for the N-doped film. The studied films are exceptionally stable, keeping their oxidation properties almost unchanged after five degradation cycles, with a special remark for the N-doped film (the degradation efficiency around 93 %). The role of ITO substrate in charge carriers separation was investigated, based on the allowed band edges values, determined both for the films and ITO.

Enhancement of ferroelectricity in chemical-solution-deposited ZrO2 thin films through fine phase transition control

Recent studies have highlighted the ferroelectric potential of ZrO2 thin films, which offer advantages over HfO2-based ferroelectric materials, such as lower thermal budget and greater natural abundance. In this research, pure ZrO2 ferroelectric thin films were fabricated on Si substrates using chemical solution deposition with all-inorganic precursors. We explored the impacts of film thickness and HfO2 seed layers on phase transition and ferroelectric properties. Notably, an 11 nm thick ZrO2 film exhibited ferroelectric behavior with a remanent polarization of 12.6 μC/cm2. Due to the combined effects of tensile stress and surface energy, the increase in thickness to 30 nm led to a phase transition from the orthorhombic phase to the monoclinic phase and a resultant decrease in remanent polarization. Additionally, the introduction of a HfO2 seed layer facilitated the crystallization of the ferroelectric o-phase, enhancing the remanent polarization to 16.5 μC/cm2 in our ∼8 nm thick ZrO2 thin film with a ∼2 nm thick HfO2 seed layer. These findings provide valuable insights into optimizing ferroelectric properties in ZrO2 thin films through phase transition control.

Photocatalytic Activities of Methylene Blue Using ZrO2 Thin Films at Different Annealing Temperatures

Tetragonal ZrO2, synthesized by the sol–gel method and dip-coating technique, was found to be photocatalytically active for the degradation of methylene blue. The ZrO2 thin films were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and UV-vis spectroscopy. The photocatalytic degradation of methylene blue was carried out with this material. We identified the tetragonal phase in ZrO2 thin film at different annealing temperatures from 400 °C to 550 °C. The XRD study indicated that the films were monocrystalline in nature with preferred grain orientation along (011) plane and exhibited a tetragonal crystal structure. The crystallite size of the films increased with increasing annealing temperature. FTIR explained the bonding nature and confirmed the formation of the composite. UV-Vis showed the optical absorbance was high in the visible region and the optical band gap value increased with annealing temperature. The photocatalytic experimental results revealed that ZrO2 thin films degraded MB by 20%, 24%, 29%, and 36%, with annealing temperatures of 400 °C at 550 °C for 10 h, respectively. Our results provide useful insights into the development of photocatalytic materials and degradation of methylene blue.

Removal and photocatalytic degradation of methylene blue on ZrO2 thin films modified with Anderson-Polioxometalates (Cr3+, Co3+, Cu2+): An experimental and theoretical study

In this work, several ZrO2 thin films modified with Anderson-type polyoxomolybdates (POMs) with general formula (NH4)6-n[XMo6O24H6]-6+n where X = Co3+, Cr3+ and, Cu2+ were prepared. Thin films were characterized through SEM and EDX assay, UV–Vis diffuse reflectance and Fourier Transform Infrared (FTIR) assay. The optical bandgap of ZrO2 thin films was determined to be 3.25 eV, while the modified thin films showed a red shift in the optical activity compared with bare ZrO2 thin films. Methylene Blue (MB) adsorption studies showed that Freundlich isotherm describes properly the experimental data for modified-ZrO2 thin films. Besides, the kinetic results showed the MB adsorption of modified-ZrO2 thin films was superior to bare ZrO2 thin film. The adsorption rate values (K2) of the pseudo-second order model follow these trend ZrO2/CrPOM > ZrO2/CoPOM > ZrO2/CuPOM > ZrO2. The photocatalytic activity of the thin films for MB decomposition under UV and Visible irradiation was studied. Among all the catalysts, the ZrO2 thin films showed the lowest photocatalytic degradation rate kap value (kap = 1.5 × 10−3 min−1), while the best result was obtained for ZrO2/CrPOM thin films (kap = 5.7 × 10−3 min−1) under UV irradiation. Besides, this was the only catalyst efficiently active in MB degradation under visible irradiation, these materials reach 10.4 % after 100 min under visible irradiation. Finally, chemical calculations supported the observed results, by means of TDDFT, EDA analysis, Fukui function and periodic DFT calculations.

Improved resistive switching characteristics of solution processed ZrO2/SnO2 bilayer RRAM via oxygen vacancy differential

In this study, a solution-processed bilayer structure ZrO2/SnO2 resistive switching (RS) random access memory (RRAM) is presented for the first time. The precursors of SnO2 and ZrO2 are Tin(Ⅱ) acetylacetonate (Sn(AcAc)2) and zirconium acetylacetonate (Zr(C5H7O2)4), respectively. The top electrode was deposited with Ti using an E-beam evaporator, and the bottom electrode used an indium–tin–oxide glass wafer. We created three devices: SnO2 single-layer, ZrO2 single-layer, and ZrO2/SnO2 bilayer devices, to compare RS characteristics such as the I–V curve and endurance properties. The SnO2 and ZrO2 single-layer devices showed on/off ratios of approximately 2 and 51, respectively, along with endurance switching cycles exceeding 50 and 100 DC cycles. The bilayer device attained stable RS characteristics over 120 DC endurance switching cycles and increased on/off ratio ∼2.97 × 102. Additionally, the ZrO2/SnO2 bilayer bipolar switching mechanism was explained by considering the Gibbs free energy (ΔG o) difference in the ZrO2 and SnO2 layers, where the formation and rupture of conductive filaments were caused by oxygen vacancies. The disparity in the concentration of oxygen vacancies, as indicated by the Gibbs free energy difference between ZrO2 (ΔG o = −1100 kJ mol−1) and SnO2 (ΔG o = −842.91 kJ mol−1) implied that ZrO2 exhibited a higher abundance of oxygen vacancies compared to SnO2, resulting in improved endurance and on/off ratio. X-ray photoelectron spectroscopy analyzed oxygen vacancies in ZrO2 and SnO2 thin films. The resistance switching characteristics were improved due to the bilayer structure, which combines a higher oxygen vacancy concentration in one layer with a lower oxygen vacancy concentration in the switching layer. This configuration reduces the escape of oxygen vacancies to the electrode during RS.

Phase transitions in ferroelectric ZrO2 thin films

In this work, the formation of the orthorhombic phase of ZrO2 together with the minor monoclinic phase were elucidated by X-ray diffraction and transmission electron microscopy. Moreover, oxidized W can be responsible for the formation of oxygen vacancies in the ZrO2 through oxygen scavenging. The ferroelectric properties of the W/ZrO2/W film capacitors were investigated through piezoresponse force microscopy (PFM) and polarization-voltage measurements.A second-order phase transition from the polar orthorhombic phase to the non-polar tetragonal phase was observed. Density functional theory calculations confirm our experimental results and propose that oxygen vacancies are responsible for the Curie–Weiss temperature of 130 °C, significantly lower than the theoretical value for the bulk.

Voltage-controlled magnetic anisotropy effect through a high-k MgO/ZrO2/MgO hybrid tunneling barrier

We investigated the voltage-controlled magnetic anisotropy (VCMA) effect in epitaxial magnetic tunnel junctions (MTJs) with a hybrid MgO/ZrO2/MgO tunnel barrier. A metastable cubic ZrO2(001) thin film was successfully grown on a MgO(001) layer, leading to the high dielectric constant of 26.5. Using the hybrid tunneling barrier, we achieved the large VCMA coefficient of −350 fJ V−1 m−1, which is 70% larger than that observed in the magnetic tunnel junction with the single MgO barrier. Introduction of crystalline high-k dielectric tunneling barrier can open up new pathways to improving the VCMA properties in MTJs for voltage-driven spintronic devices.