Tantalum Oxide Thin Films Research Articles

Synthesis of tantalum oxide thin films using RF magnetron sputtering for RRAM application

Resistive Random Access Memory (RRAM) is a prominent contender in the realm of emerging non-volatile memory technologies owing to its numerous advantages like simple structure, low power usage, high speed, and exceptional scalability. In the current study, RRAM device was fabricated using tantalum oxide (TaOx) as a resistive switching insulating oxide layer, which was sandwiched between two conducting electrodes, namely Ag and ITO. RF magnetron sputtering was used to deposit the insulating layer of TaOx at room temperature on the ITO substrate. Further, X-ray reflectivity and hard X-ray photoelectron spectroscopy analyses were conducted to find the thickness, roughness, and elemental composition of the deposited TaOx films. Using a semiconductor analyzer, the RRAM cell's first DC switching characteristics were determined. The data acquired exhibited a resistance ratio (R HRS/R LRS) of 120 showing a good distinction between the two-resistance states. Additionally, a thorough investigation was conducted to examine the electrical conduction mechanism occurring inside the fabricated RRAM device.

Reduction of mechanical losses in ion-beam sputtered tantalum oxide thin films via partial crystallization

This study explores the impact of crystalline fraction on the mechanical losses of amorphous tantalum oxide (tantala, Ta2O5) thin films intended for gravitational wave detectors. We use ion beam sputtering technique to prepare a series of samples, which are then subjected to controlled thermal annealing to achieve varying degrees of crystallized fraction. The microscopic structure of the annealed samples is characterized by combining different analytical techniques. Our investigation reveals that the amorphous films comprise randomly distributed crystalline grains, whose density and average size depends on the duration of thermal treatment. To assess mechanical losses of the coatings, a gentle nodal suspension system is applied. Remarkably, a substantial reduction of approximately 20% in the coating’s mechanical loss angle with respect to annealed amorphous coatings is observed for samples exhibiting a crystalline fraction of around 5%. This improvement may lead to the definition of alternative thermal treatments to improve the mechanical performances of coatings for gravitational wave detectors or other highly sensitive optical experiments. However the reduction in mechanical losses comes at the expense of an increase in optical scattering. The possibility of reducing the optical losses to the level required by gravitational interferometers by modifying the grain size distribution via appropriate annealing treatments is discussed.

Enhanced Electrical and Optical Properties of Bismuth Tantalum Oxide Thin Films through Graphene Oxide Doping.

In this study, a hybrid thin film was fabricated by doping graphene oxide in a bismuth tantalum oxide solution in the sol-gel state. The thin film was produced by a brush-coating process. The graphene oxide doping ratios used were 0, 5, and 15 wt %. In the process of producing the thin film, the prepared sol-gel solution generates contraction forces, owing to the shear stress from the bristles of the brush, forming a microgroove structure. This structure was confirmed through atomic force microscopy, transmission electron microscopy, and energy-dispersive spectroscopy analyses. As a result of line profile analysis in atomic force microscopy, the groove heights of the thin film surface at 0, 5, and 15 wt % doping were 110, 130, and 160 nm, respectively, and the width of all grooves was 1 μm. The width of all thin films was approximately 1 μm, and microgrooves were confirmed. Moreover, the hybrid thin-film formation was confirmed by X-ray photoelectron spectroscopy. By comparing the electrical properties of the bismuth tantalum oxide thin film without graphene oxide doping and the thin film doped with 15 wt % graphene oxide, it was demonstrated that the electro-optical properties increased excellently with graphene oxide doping. Typically, the threshold voltage was reduced by approximately 0.26 V. Based on these observations, graphene oxide doped bismuth tantalum oxide hybrid thin films can be considered as promising candidates for thin-film applications in next-generation displays.

Modulation of electrical properties of sputtered Ta2O5 films by variation of RF power and substrate temperature

Dielectric thin films are important building blocks of microelectronic devices, and hence, research on the development of high-k dielectric thin films has drawn tremendous research interest. In this research, thin films of tantalum oxide (Ta2O5), a high-k dielectric material, are deposited on the Si substrate by the radio frequency (RF) magnetron sputtering technique. During the deposition of Ta2O5 thin film, the sputtering parameters such as sputtering power and substrate temperature were systematically varied, and post-deposition structural, morphological, and electrical properties of sputtered Ta2O5 films are studied by x-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscope, capacitance–voltage (C-V) and current–voltage (I-V) measurement techniques. The annealed Ta2O5 thin film at the temperature of 900 °C for 1 h possesses polycrystalline nature with β—phase orthorhombic crystal structure. The film deposited at 150 W and substrate temperature at room temperature has shown comparatively lower surface roughness, which depicts the energy, and mobility of adatoms greatly influenced by RF power and substrate temperature. With the increase in sputtering power, the oxide charge density (Qox) is found to increase. On the other hand, Qox is found to decrease with the increase in substrate temperature. The film deposited at RF power of 150 W and substrate temperature of 300 °C is found to be of high dielectric constant, low oxide and interface charge density, and lower leakage current.

Aluminum tantalum oxide thin films deposited at low temperature by pulsed direct current reactive magnetron sputtering for dielectric applications

This research aims at studying aluminum tantalum oxide thin films (AlxTayOz) deposited at low temperature for dielectric applications. These ternary oxide layers are synthesized at 180 °C by physical vapor deposition (PVD), specifically the mid-frequency pulsed direct current reactive magnetron sputtering. The deposition process uses targets made of a mixture of aluminum and tantalum in various proportions. Four target compositions are studied containing 95 at.%, 90 at.%, 80 at.%, and 70 at.% of aluminum, corresponding to 5 at.%, 10 at.%, 20 at.%, and 30 at.% of tantalum, respectively. The ternary oxide thin films of AlxTayOz are compared to aluminum oxide (AlxOz) and tantalum oxide (TayOz) layers produced in the same experimental conditions. The AlxTayOz thin films are dense, uniform, and amorphous regardless of the experimental conditions used in this study. Their chemical composition changes as a function of the target composition. The oxygen flow used during deposition also affects the chemical composition of the oxide layers and the deposition rate. The oxide thin films with tantalum are deposited at higher deposition rates and contain more oxygen. Tantalum also promotes the amorphization of the oxide layers. The highest dielectric strength is measured for the thin film containing a low amount of tantalum combined with a high amount of oxygen.

Tantalum Oxide Thin Films Sputter-Deposited by Oxygen Gas Pulsing

Tantalum oxide thin films are deposited by DC reactive magnetron sputtering from a tantalum metallic target and argon + oxygen. The oxygen gas is pulsed during the deposition with a constant pulsing period T = 10 s, whereas the introduction time of the reactive gas, namely the tON injection time, is systematically changed from 0 to 100% of T. Therefore, composition of as-deposited TaOx films is continuously changed from pure metallic tantalum to the over-stoichiometric Ta2O5 material. Films adopt the body-centered cubic structure (metallic Ta) for the lowest tON injection time values (oxygen stoichiometry x < 1.0) and become amorphous for the longest ones. It is shown that the tON injection time is a key parameter to deposit either homogeneous tantalum oxides, or periodic Ta/TaOx multilayers with alternations close to 3 nm. Optical transmittance in the visible region of the film/glass substrate system and electrical conductivity vs. temperature both exhibit a gradual evolution from metallic (σ300K = 8.17 × 105 S m−1 with an opaque behavior) to semiconducting (σ300K = 1.97 × 103 S m−1 with a semi-transparent transmittance) and finally to dielectric properties (σ300K < 10−5 S m−1 for interferential films) as a function of the oxygen concentration in the films.

Investigations of endurance and retention in tantalum oxide based memristor

Transparent neuromorphic electronics are gaining attention due the advantages of low-power operation, artificial self-learning synapses, and invisible circuits. Memristor plays a critical role in realizing these devices where the resistive state is continuously modified with application of external perturbations such as electric field, current, temperature and light. Endurance and retention are very important parameters for the repeatability and reliability of the device. Here, we have fabricated a memristor based on amorphous tantalum oxide thin films on transparent conducting oxide (TCO) substrate, using a physical vapor deposition technique. The structural quality of these films was confirmed by various characterization techniques namely Raman spectroscopy, UV–Vis spectroscopy, Scanning Electron Microscopy, Atomic Force Microscopy, and X-Ray Reflectivity. The device characteristics were measured using a semiconductor characterization system (SCS 4200). The influence of morphology, device thicknesses, and the nature of top and bottom electrodes has been investigated in detail to enhance the endurance and retention properties.

Effect of Oxygen Content on the Properties of Sputtered TaOx Electrolyte Film in All-Solid-State Electrochromic Devices

Tantalum oxide (TaOx) thin films are one of the commonly used solid electrolytes in inorganic all-solid-state electrochromic devices (ECDs). The chemical composition and microstructure of TaOx films have a crucial influence on its electron blocking and ion transport properties in all-solid-state ECDs. In this work, various oxygen flux was used to deposit the TaOx films with different compositions and microstructures by pulsed direct current (p-DC) reactive magnetron sputtering. The structural properties, morphologies, chemical compositions, optical properties, electron blocking, and ionic conductive properties of the TaOx films were systematically investigated. The results show that in a certain range, the higher the oxygen flux, the stronger the ion transport ability of TaOx and the lower the electronic conductivity, which could be attributed to the loose structure and smaller number of oxygen vacancies of the films, respectively. Moreover, an all-solid-state ECD with the multilayer structure of glass/ITO/WO3/Li/TaOx/NiO/ITO was also fabricated by the magnetron sputtering method. The device exhibited excellent comprehensive electrochromic properties including high optical modulation, large coloring efficiency, fast response (especially bleaching process), and good cycle stability.

Tantalum Oxide Coating of Ni-rich Cathode Active Material via Atomic Layer Deposition and its Influence on Gas Evolution and Electrochemical Performance in the Early and Advanced Stages of Degradation

Detrimental side-reactions of Ni-rich cathode active materials (CAMs) with the electrolyte have historically impeded the extension of the utilized voltage window to higher upper cut-off voltages. Doping and coating approaches are studied widely to further improve these materials and to reduce the intensity of bulk and surface degradation but suffer from poor control of film thickness and homogeneity, leading to partial doping of the bulk. We herein report the singular effect of a tantalum oxide (Ta2O5) thin film on Li[Ni0.8Mn0.1Co0.1]O2 (NMC811), generated by atomic layer deposition, offering the possibility of a high-level homogeneity and thickness control. After chemical analysis using X-ray photoelectron spectroscopy the composition of the deposited thin film is identified as a lithium tantalate chemistry (LiTaO3). At an early degradation stage, clear improvements directly attributed to the coating, such as suppressed exothermic side-reactions (−51%), reduced released gas amounts (−14.8%) and less charge-transfer resistance growth (2× lower) are observed. However, at an advanced degradation stage, the materials show similar cycle life, as well as similar gassing behavior and an even higher charge-transfer resistance growth as compared to the uncoated material. This study highlights the necessity of bulk stabilization and identifies the effect of surface coatings on undoped NMC811 without any doping influence.

In vitro biocompatibility and degradation assessment of tantalum oxide coated Mg alloy as biodegradable implants

In the present study, the sputtering process deposited tantalum oxide thin film onto AZ31B alloy, and the biocompatibility and degradation resistance were evaluated. The phase analysis by X-ray diffraction (XRD) and transmission electron microscopy (TEM) was carried out to understand the Ta-based thin films’ crystalline and amorphous nature thin film. The thin film surface chemical composition was investigated by X-ray Photoelectron Spectroscopy (XPS) which showed the elemental signals of O, Ta without any other impurities. Contact angle measurements verified the hydrophobic nature of the coated specimens. The corrosion studies revealed that corrosion resistance was significantly enhanced for the Ta-based thin-film coated Mg alloys than the uncoated bare counterpart by reducing corrosion current density from 2.886 × 10−4 to 1.20 × 10−5 A/cm2. Bioactivity of the coated specimens in SBF immersion showed apatite formation in 5 days. The hemocompatibility studies of the coatings showed the echinocytes morphology of the RBCs. In vitro, MTT assay exhibited more significant cell proliferation and cell viability of 100% at 7 days of incubation. The cell morphology studies showed improved cell attachment and cell growth by controlling magnesium ions' release into the cell culture media.

Plasma Enhanced Atomic Layer Deposition of Tantalum (V) Oxide

The tantalum oxide thin films are promising materials for various applications: as coatings in optical devices, as dielectric layers for micro and nanoelectronics, and for thin-films solid-state lithium-ion batteries (SSLIBs). This article is dedicated to the Ta-O thin-film system synthesis by the atomic layer deposition (ALD) which allows to deposit high quality films and coatings with excellent uniformity and conformality. Tantalum (V) ethoxide (Ta(OEt)5) and remote oxygen plasma were used as tantalum-containing reagent and oxidizing co-reagent, respectively. The influence of deposition parameters (reactor and evaporator temperature, pulse and purge times) on the growth rate were studied. The thickness of the films were measured by spectroscopic ellipsometry, scanning electron microscopy and X-ray reflectometry. The temperature range of the ALD window was 250–300 °C, the growth per cycle was about 0.05 nm/cycle. Different morphology of films deposited on silicon and stainless steel was found. According to the X-ray diffraction data, the as-prepared films were amorphous. But the heat treatment study shows crystallization at 800 °C with the formation of the polycrystalline Ta2O5 phase with a rhombic structural type (Pmm2). The results of the X-ray reflectometry show the Ta-O films’ density is 7.98 g/cm3, which is close to the density of crystalline Ta2O5 of the rhombic structure (8.18 g/cm3). The obtained thin films have a low roughness and high uniformity. The chemical composition of the surface and bulk of Ta-O coatings was studied by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. Surface of the films contain Ta2O5 and some carbon contamination, but the bulk of the films does not contain carbon and any precursor residues. Cyclic voltammetry (CVA) showed that there is no current increase for tantalum (V) oxide in a potential window of 3–4.2 V and has prospects of use as protective coatings for cathode materials of SSLIBs.

New Volatile Tantalum Imido Precursors with Carboxamide Ligands.

A series of Ta(V) tBu-imido/N-alkoxy carboxamide complexes, TaCl2(NtBu)(pyridine)(edpa) (1), TaCl(NtBu)(edpa)2 (2), Ta(NtBu)(edpa)3 (3), TaCl2(NtBu)(pyridine)(mdpa) (4), and Ta(NtBu)(mdpa)3 (5), were successfully synthesized by metathesis reactions between Ta(NtBu)Cl3(py)2 and several equivalents of Na(edpa) (edpaH = N-ethoxy-2,2-dimethylpropanamide) and Na(mdpa) (mdpaH = N-methoxy-2,2-dimethylpropanamide). Furthermore, complexes 3 and 5 were simply transformed to new dimeric structures [Ta(μ2–O)(edpa)3]2 (6) and [Ta(μ2–O)(mdpa)3]2 (7) with the elimination of the NtBu imido group by air exposure. Compounds 1–7 were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that complexes 3 and 5 have a distorted pentagonal bipyramidal geometry around the central Ta atom, with three monoanionic bidentate N-alkoxy carboxamide ligands and one tBu imido ligand saturating the coordination of tantalum ions. TGA revealed that complexes 3 and 5 had superior thermal characteristics and stability. These complexes could potentially be applied as precursors for tantalum oxide thin films.

Dielectric properties investigation of a compound based on atomic layer deposited multi-layer structure

This study presents dielectric properties investigation of hafnium oxide (HfOx), aluminum oxide (AlOx) and tantalum oxide (TaOx) thin films and HfAlTaOx compound based on their multilayer structure. The thickness of all films under study was 40 nm. The investigated films were produced from metal-organic precursors by Plasma Enhanced Atomic Layer Deposition (PEALD). Based on the dielectrics mentioned above, we produced Metal – Insulator – Metal (MIM) capacitors and researched their properties. Dielectric constant for HfOx, AlOx, TaOx and HfAlTaOx was 20, 9, 31 and 13, correspondingly. Volumetric efficiency of MIM capacitors based on HfOx, AlOx, TaOx and HfAlTaOx was 4.4 nF/mm2, 2 nF/mm2, 6.8 nF/mm2 and 2.9 nF/mm2, correspondingly. Dielectric strength of HfAlTaOx compound was significantly higher (8.2 MV/cm) compared to other dielectrics: HfOx (3.6 MV/cm), AlOx (6.4 MV/cm), TaOx (1.5 MV/cm). The greatest values were observed in the compound of significantly higher dielectric strength which is comparable to silicon oxide. This study was the first to demonstrate the advantages of the produced compound, such as high dielectric constant and dielectric strength.

Laser synthesis of non-volatile memristor structures based on tantalum oxide thin films

The amorphous thin TaOx films (x ≤ 5) of different thicknesses with different levels of oxygen vacancy content, which are promising for use as an active region of non-volatile memristors, were fabricated by the pulsed laser deposition in a drop-free mode on the c-sapphire substrates. The films were obtained from tantalum metal targets at substrate temperatures of 25 °C and 350 °C in the oxygen pressure range from 0.5 to 50 mTorr. The relationship between the partial oxygen pressure and the optical, electrical, and chemical properties of the films was studied. It was found that the amorphous TaOx phase, which is a source of defects associated with oxygen deficiency, required for the creation of memristors, appears only at low oxygen pressures in the chamber (~ 5 × 10−4 Torr), this leads to low values resistivity in the films (~ 10−3 Ohm · cm). Memristor structures Ag(Pt)/TaOx/TaOy/Ta/c-Al2O3 (x > y) in cross-bar geometry have been created that do not require electroforming, due to the choice of design and deposition conditions. Memristor using two mechanisms of resistive switching based on oxygen vacancies and silver cations showed very reliable RS performance with memory window performance RON/ROFF ~ 103 and RESET operating voltage ~ 1 V.

Picosecond multilevel resistive switching in tantalum oxide thin films

The increasing demand for high-density data storage leads to an increasing interest in novel memory concepts with high scalability and the opportunity of storing multiple bits in one cell. A promising candidate is the redox-based resistive switch repositing the information in form of different resistance states. For reliable programming, the underlying physical parameters need to be understood. We reveal that the programmable resistance states are linked to internal series resistances and the fundamental nonlinear switching kinetics. The switching kinetics of hbox {Ta}_2 hbox {O}_5-based cells was investigated in a wide range over 15 orders of magnitude from 10^5 s to 250 ps. The capacitive charging time of our device limits the direct observation of the set time below 770 ps, however, we found indication for an intrinsic switching speed of 10 ps at a stimulus of 3 V. On all time scales, multi-bit data storage capabilities were demonstrated. The elucidated link between fundamental material properties and multi-bit data storage paves the way for designing resistive switches for memory and neuromorphic applications.

Influence of substrate cooling on ion conductivity of tantalum oxide thin films prepared by reactive sputtering using water vapor injection

We studied a reactive sputtering technique that involves substrate cooling with liquid nitrogen and water vapor injection into the substrate surface to deposit Ta2O5 solid electrolyte thin films. The ion conductivities of the tantalum oxide films increased upon substrate cooling, and the maximum conductivities of approximately 10−3 S/m were obtained at substrate temperatures of −120°C and −80°C. The deposition rate increased by substrate cooling and high deposition rates of 30–50 nm/min were obtained at substrate temperatures of −80 °C to −170 °C. According to these results, this sputtering technique is highly effective for improving ion conductivity and the deposition rate of Ta2O5 films.

Fabrication of a Novel Ta(Zn)O Thin Film on Titanium by Magnetron Sputtering and Plasma Electrolytic Oxidation for Cell Biocompatibilities and Antibacterial Applications

Pure titanium (Ti) and titanium alloys are widely used as artificial implant materials for biomedical applications. The excellent biocompatibility of Ti has been attributed to the presence of a natural or artificial surface layer of titanium dioxide. Zinc oxide and tantalum oxide thin films are recognized due to their outstanding antibacterial properties. In this study, high power impulse magnetron sputtering (HiPIMS) was used for the deposition of tantalum oxide and zinc-doped Ta(Zn)O thin films on Ti with rough and porous surface, which was pretreated by plasma electrolytic oxidation (PEO). Surface morphology, antibacterial property as well as cell biocompatibility were analyzed. The antibacterial effect was studied individually for the Gram-positive and Gram-negative bacteria Staphylococcus aureus (S. aureus) and Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans). The deposited Ta (Zn)O coating was composed of amorphous tantalum oxide and crystalline ZnO. The antibacterial results on the tantalum oxide and Ta(Zn)O coated Ti indicated a significant inhibition of both S. aureus and A. actinomycetemcomitans bacteria when compared with the uncoated Ti samples. The deposited Ta(Zn)O showed the best antibacterial performance. The Ta(Zn)O coated Ti showed lower level of the cell viability in MG-63 cells compared to other groups, indicating that Zn-doped Ta(Zn)O coatings may restrict the cell viability of hard tissue-derived MG-63 cells. However, the biocompatibility tests demonstrated that the tantalum oxide and Ta(Zn)O coatings improved cell attachment and cell growth in human skin fibroblasts. The cytotoxicity was found similar between the Ta2O5 and Ta(Zn)O coated Ti. By adopting a first PEO surface modification and a subsequent HiPIMS coating deposition, we synthetized amorphous tantalum oxide and Ta(Zn)O coatings that improved titanium surface properties and morphologies, making them a good surface treatment for titanium-based implants.

Antimicrobial effects by silver–indium–tantalum oxide thin film in visible light

This study focuses on the antimicrobial effects in silver-indium-tantalum oxide (Ag–InTaO) thin films. A stack of alternated layers of Ag (7 ​nm), In2O3 (14 ​nm) and Ta2O5 (10 ​nm) was sequentially deposited by sputtering. Then this as-deposited stack of films was rapidly annealed at three selected temperatures 700, 800 or 900 ​°C for 5 ​min to allow the formation of complex oxides. Results from material characterization indicate that annealing help to form complex oxides, intermetallic compounds and Ag particles on the top surface. These features lead to the improved antimicrobial effect against E. Coli. under visible light by Ag–InTaO.

Absorption, discharge, and internal partitioning behavior of hydrogen in the tantalum and tantalum oxide system investigated by in situ oxidation SIMS and ab initio calculations

Hydrogen behavior in tantalum and tantalum oxide thin films was examined using the in situ oxidation secondary ion mass spectrometry (in situ oxidation SIMS) method previously developed by the authors. Oxidation of Ta films by the introduction of O2 into the sputter deposition chamber immediately after film growth was found to reduce the amount of H absorbed in the Ta films by 2.7 times for samples exposed to lab air at ambient temperature; the difference increased to 4.8 times for samples exposed to air at 300 °C. From these results, it is apparent that Ta absorbs H from H2 or through reaction with H2O in air and that an oxide film “cap” largely stymies H absorption. To investigate the redistribution of hydrogen during oxidation of Ta, sputtered Ta films were implanted with deuterium, and some were subsequently anodized. In situ oxidation SIMS analysis of Ta2O5/Ta bilayer films created by anodization of deuterium (D)-implanted Ta films revealed no deuterium in the upper Ta2O5 portion; however, the total amount of deuterium detected in the underlying Ta layer of the anodized samples was close to the total amount of deuterium measured in the Ta layer of a nonanodized, D-implanted Ta film. These results indicate that during anodization, D is concentrated in the residual metal region as it is excluded from the growing oxide film. Ab initio calculations of H interstitial defects in Ta and Ta2O5 revealed that the heat of formation, ΔH, for H interstitial defects in Ta is 1.31 eV lower than that of Ta2O5; this result is consistent with the observed H blocking property of oxide films and the observed redistribution of D from oxide to metal during anodization.

Tantalum oxide thin films for electrochemical pH sensor

Present work demonstrates the fabrication and utilization of tantalum oxide (Ta2O5) thin films as prominent pH sensing electrode material. Ta2O5 film of 1 μm thickness was deposited on glass substrates using physical vapor deposition technique. Structural and morphological studies were performed on these thin films. Electrochemical studies were carried out on these films using amperometry, linear sweep voltammetry and cyclic voltammetry techniques. These Ta2O5 coated substrates were found to be sensitive to various assorted pH solutions and hence were used as pH sensing electrode. The performance of the electrode was studied in terms of stability, reusability and selectivity. Results reveal that the films were found to be suitable pH sensing material in 1.0–12.0 pH range. The sensing electrodes were found to be reliable and reusable with less than 5 s response time.