Electrical characteristics of Ti-O/Ta2O5 thin film sputtered on Ta/Ti/Al2O3 substrate

The electrical characteristics of Ti-O/Ta₂O₅ films sputtered on Ta/Ti/Al₂O₃ substrate were investigated. Ta (tantalum) was used for the bottom and upper electrodes for the purpose of simplifying the fabrication process and Al₂O₃ substrates were used, which are needed in integral passive devices. Ta/Ti-O/Ta₂O₅/Ta/Ti/Al₂O₃ capacitors were annealed at 700 °C for 60 s in vacuum. The X-ray diffraction pattern (XRD) results showed that as-deposited Ta had a highly preferred orientation, but Ta₂O₅ film had amorphous structure, which was transformed to crystallization structure by rapid thermal heat treatment. We examined the log J-E and C-V characteristics of the dielectric thin films deposited on the Ta bottom electrode. From these results, we concluded that the leakage current could be reduced by introducing a Ti-O buffer layer. The conduction mechanisms of Ta/Ti-O/Ta₂O₅/Ta/Ti/Al₂O₃ capacitors could be interpreted appropriately by hopping conduction in lower field (E<1×10⁵ V/cm) and space-charge-limited current in higher fields (1×10⁵ V/cm<E).     

Overview about the optical properties and mechanical stress of different dielectric thin films produced by reactive-low-voltage-ion-plating

Thin films of Ta₂O₅, Nb₂O₅, and HfO₂ were deposited by reactive-low-voltage-ion-plating (RLVIP) on unheated glass and silicon substrates. The film thickness was about 200 nm. Optical properties as well as mechanical film stress of these layers were investigated in dependence of various deposition parameters, i.e. arc current and oxygen partial pressure. For an arc current in the range between 40 and 50 A and an oxygen partial pressure of at least 11 · 10^− 4 mbar good results were obtained. The refractive index and film thickness were calculated from spectrophotometric transmission data using the Swanepoel theory. For example at 550 nm wavelength the refractive index for thin RLVIP-Nb₂O₅-films was found to be n₅₅₀ = 2.40. The optical absorption was obtained by photo-thermal deflection spectrometry. For the investigated materials absorption coefficients in the range of k = 5 · 10^− 4 at 515 nm wavelength were measured. The mechanical film stress was determined by measuring the difference in bending of silicon substrates before and after the deposition process. For dense films, i.e. no water vapour sorption on atmosphere, the mechanical film stress was always compressive with values of some hundred MPa. In case of films deposited with higher arc currents (I_arc > 60A) and lower oxygen pressure (< 15 · 10^− 4 mbar) the influence of a post deposition heat treatment at 350 °C for 4 h on air was also investigated. For these films the properties could clearly be improved by such treatment. However, by using lower arc currents and higher oxygen partial pressure during the ion plating process, immediately dense and environmental stable films with good optical as well as mechanical properties could be achieved without post deposition heat treatment. All the results obtained will be presented in graphs and diagrams.     

Conducting and topographic AFM analysis of Hf-doped and Al-doped Ta2O5 films

A conductive atomic force microscopy (C-AFM) has been used to study conductivity and electrical degradation of ultrathin (4 nm) Hf- and Al-doped Ta₂O₅ at the nanometer scale. The hardness testing has been also performed using the force measuring ability of the AFM. Since the size of the analyzed area is very small, features which are not visible by macroscopic tests are observed: extremely low leakage current (~ pA) up to significantly higher than the fields during standard current-voltage measurements; charge trapping/detrapping processes manifesting as current peaks at pre-breakdown voltages. Hf and Al addition improves the local conductivity of Ta₂O₅, provokes modification of the leakage current mechanism, and is effective in extending the potential of pure Ta₂O₅ as a high-k material at the nanoscale. The results point to a decisive role of the type of the dopant on the electrical and mechanical properties of the films and their local response to short term microwave irradiation. Hf-doped Ta₂O₅ exhibits excellent electrical stability and high hardness. Al doping provides more plastic films with large electrical inhomogeneities; the microwave treatment at room temperature is a way to improve these parameters to a level comparable to those of Hf-doped films.     

等离子体电解氧化法制备多孔TiO2/V2O5复合物膜层及其增强光催化产氢活性

较差的光催化产氢效率极大地阻碍了TiO₂光催化剂的工业化应用。为此,本文在含有NH₄VO₃的磷酸盐溶液中,采用等离子体电解氧化(PEO)法制备了多孔TiO₂/V₂O₅复合膜光催化剂,通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)、X射线光电子谱(XPS)和紫外可见漫反射光谱(UV-Vis DRS)对其组成、结构及光吸收性质进行了表征,并采用气相色谱评价了薄膜催化剂的光催化产氢性能,研究了电解液中NH₄VO₃含量对膜的结构、组成和光催化产氢性能的影响。结果表明:复合膜催化剂主要由锐钛矿和金红石型TiO₂组成,具有微孔结构,V₂O₅主要以无定形形式存在于膜中,与TiO₂有很强的相互作用,影响TiO₂的晶面间距。研究发现,元素V抑制了TiO₂的结晶和金红石型TiO₂的形成,扩大了薄膜的光学吸收范围。针对Na₂S+ Na₂SO₃溶液中的光催化产氢性能的研究显示,在质量浓度为1 g/L NH₄VO₃的电解液中制备的TiO₂/V₂O₅薄膜的光催化活性最高,优于近年来报道的其他光催化剂。光催化重复实验表明,该复合膜催化剂具有较高的稳定性和较为恒定的光催化活性。     

Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al₂O₃-ZrO₂ composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO₂ film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al₂O₃-ZrO₂ film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO₂-Al₂O₃ film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10⁻⁷ A/cm² at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.     

Gravitational waves detector mirrors: Spectroscopic ellipsometry study of Ta2O5 films on SiO2 substrates

A stack of Ta₂O₅/SiO₂ layers is presently used as coating layer of mirrors in interferometric detectors for gravitational waves. The sensitivity of these detectors is limited in the 50-300 Hz frequency range by the mirror thermal noise, and it was suggested that mechanical losses in the Ta₂O₅ are the dominant source of noise. We focus here on Spectroscopic Ellipsometry (SE) results (in the 0.75 ÷ 5 eV spectral range) obtained on high quality Ta₂O₅ films deposited on SiO₂ substrates by Double Ion Beam Sputtering at the Laboratoire des Matériaux Avancés (Lyon, France). The films are extremely flat as indicated by the 0.2 nm RMS roughness determined by Atomic Force Microscopy (AFM) on (20 × 20) μm² areas. The comparison of the optical properties determined by SE with literature data, corroborated by X-ray Photoelectron Spectroscopy (XPS) data, suggests that the films present a non-ideal bulk stoichiometry and/or some degree of nanoporosity. The possible influence of an interface layer is also discussed.     

Preparation and tribological properties of polyurethane/α-aluminum oxide hybrid films

This study focused on the preparation and tribological properties of polyurethane/α-aluminum oxide (PU/α-Al₂O₃) hybrid films. PU/α-Al₂O₃ hybrid films containing various nanoscaled α-Al₂O₃ contents were prepared by an effectively mechanical stirring method. The tribological properties of PU/α-Al₂O₃ hybrid films were investigated by a TABER type abrasion tester after 2000 cycles. The results of abrasion tests showed the abrasion resistance of the PU/α-Al₂O₃ hybrid film was increased as the α-Al₂O₃ content was increased. The abrasion resistance of the PU/α-Al₂O₃ hybrid film was significantly improved up to 27.4% by adding 2 wt.% nanoscaled α-Al₂O₃ particles. The surface morphologies of PU/α-Al₂O₃ hybrid films, before and after abrasion tests, were examined by scanning electron microscopy (SEM). For the loading of 2 wt.% α-Al₂O₃ particles, the SEM image of the worn surface of the PU/α-Al₂O₃ hybrid film showed much smoother than those of pure PU film and other PU/α-Al₂O₃ hybrid films.     

Synthesis,Characterization and Photocatalytic Activity of TiO_2 Film/Bi_2O_3 Microgrid Heterojunction

TiO2 film modified by Bi2O3 microgrid array was successfully fabricated by using a microsphere lithography method.The structure and morphology of TiO2 film,Bi2O3 film and TiO2 film/Bi2O3 microgrid heterojunction were characterized through X-ray diffraction,atomic force microscopy and scanning electron microscopy.The optical transmittance spectra and the photocatalytic degradation capacity of these samples to rhodamine B were determined via ultraviolet-visible spectroscopy.The results indicated that the coupled system showed higher photocatalytic activity than pure TiO2 and Bi2O3 films under xenon lamp irradiation.The enhancement of the photocatalytic activity was ascribed to the special structure,which could improve the separation of photo-generated electrons and holes,enlarge the surface area and extend the response range of TiO2 film from ultraviolet to visible region.     

Simultaneous determination of the thermal expansion coefficient and the elastic modulus of Ta2O5 thin film using phase shifting interferometry

Abstract

This paper reports on the application of a phase shifting interferometry technique for the concurrent measurement of the thermal expansion coefficient α_f and the elastic modulus E_f /1 - V_f of Ta₂O₅ thin film. The Ta₂O₅ films were prepared by ion beam sputter deposition. The stresses in the thin films were measured with the phase shifting interferometry technique using two types of circular discs with known thermal expansion coefficients, Young's moduli and Poisson's ratios. The temperature-dependent stress behaviour of Ta₂O₅ films was obtained by heating samples in the range from room temperature to 70°C. The internal stresses of Ta₂O₅ thin films deposited on the BK-7 and Pyrex glass substrates were plotted against the stress measurement temperature, showing a linear dependence. From the slopes of the two lines in the stress versus temperature plot, the thermal expansion coefficient and the elastic modulus of Ta₂O₅ thin film are then calculated.     

Microstructure and characterization of Ni-Co/Al2O3 composite coatings by pulse reversal electrodeposit

Ni-Co/Al₂O₃ composite coatings were obtained by pulse reversal electrodeposit (PRC) and direct current electrodeposit (DC). The microstructure of the coatings was characterized by means of SEM, XRD and TEM. Hardness, wear resistance and macro residual stress of coatings were also investigated. The results showed that the microstructure and performance of the coatings were significantly affected by the electrodeposit methods and the Al₂O₃ particles content. The PRC composite coatings exhibited compact surface, high hardness and excellent wear resistance. The macro residual stress of PRC composite coatings was lower than that of DC ones. With the increasing of Al₂O₃ particles content, the hardness and wear resistance of the composite coatings increased.     

Preparation and characterization of Nb2O5-Al2O3 composite oxide formed by cathodic electroplating and anodizing

Al foil was coated with niobium oxide by cathodic electroplating and anodized in a neutral boric acid solution to achieve high capacitance in a thin film capacitor. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed the niobium oxide layer on Al to be a hydroxide-rich amorphous phase. The film was crystalline and had stoichiometric stability after annealing at temperatures up to 600 °C followed by anodizing at 500 V, and the specific capacitance of the Nb₂O₅-Al₂O₃ composite oxide was approximately 27% higher than that of Al₂O₃ without a Nb₂O₅ layer. The capacitance was quite stable to the resonance frequency. Overall, the Nb₂O₅-Al₂O₃ composite oxide film is a suitable material for thin film capacitors.     

Preparation of mesoporous tantalum oxide and its enhanced photocatalytic activity

Mesoporous Ta₂O₅ was synthesized by a surfactant-assisted sol-gel method under mild condition. Based on XRD pattern, the products, obtained by calcination at 600 and 700 °C, were found to be in the amorphous and the orthorhombic phases, respectively. The morphology and pore structure of the products were characterized by SEM, TEM and nitrogen adsorption-desorption measurements. The photocatalytic activity was evaluated by measuring the degradation of methylene blue under UV irradiation. Mesoporous orthorhombic Ta₂O₅ showed higher photocatalytic activity than that of the mesoporous sample in the amorphous state, although orthorhombic Ta₂O₅ had a lower surface area. The reason of this enhanced photocatalytic property is discussed.     

Tribological properties of WS2 composite film prepared by a two-step method

In order to extend the application range of solid lubricant WS₂, the author adopted a two-step method to prepare WS₂ film; namely, W film was first fabricated on the AISI 1045 steel by magnetron sputtering method, and then treated by low temperature ion sulfuration to obtain WS₂ composite film. XRD was used to analyze the phase structure of the WS₂ composite film; its surface and worn scar morphologies were analyzed with SEM + EDS; X-ray stress determinator was utilized to measure its residual stress; the nano-hardness and elastic modulus of WS₂ composite film were surveyed by a nano-indentation tester. The tribological properties were investigated on a ball-on-disk wear tester under dry condition. The results showed that WS₂ composite film had much better anti-friction and wear-resistance properties than the original 1045 steel and sulfurized layer.     

Synthesis of K6Ta10.8O30 nanowires by molten salt technique

The synthesis of single crystalline K₆Ta_10.8O₃₀ nanowires by molten salt method was reported for the first time. X-ray diffraction results indicated that the as-prepared products were pure phase K₆Ta_10.8O₃₀. Scanning electron microscopy and transmission electron microscopy results showed that the products consisted of wire-like nanostructures with 100-300 nm in diameter and several micrometers in length. High resolution electron microscopy and selected area electron diffraction results indicated that the K₆Ta_10.8O₃₀ nanowires were single crystalline with a growth direction of [0 0 1]. The ultraviolet-visible diffuse reflectance measurement showed that the band gap of the nanowires was about 4.1 eV. The effects of reaction temperature, time, and weight ratio of the precursor (mixture of K₂CO₃ and Ta₂O₅) to KCl salt on the morphology of the products were investigated.     

Photocatalytic degradation of formaldehyde by nanostructured TiO2 composite films

Interest in the photocatalytic oxidation of formaldehyde from contaminated wastewater is growing rapidly. The photocatalytic activity of the nanocrystalline Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film for the degradation of formaldehyde solution under visible light was discussed in this study. The films were characterised by field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy, X-ray diffraction (XRD), BET surface area, UV–Vis absorption spectroscopy, and photoluminescence spectroscopy. The FE-SEM results revealed that the Fe³⁺/F^? co-doped TiO₂–SiO₂ film was composed of uniform round-like nanoparticles or aggregates with the size range of 5–10 nm. The XRD results indicated that only the anatase phase was observed in the film. Compared with a pure TiO₂ film and a singly modified TiO₂ film, the Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film showed the best photocatalytic properties due to its strong visible light adsorption and diminished electrons-holes recombination.     

Characterization of high quality tantalum pentoxide film synthesized by oxygen plasma enhanced pulsed laser deposition

Tantalum pentoxide films were deposited on BK7 glass substrates using oxygen plasma enhanced pulsed laser deposition (OPE-PLD). X-ray diffraction, atomic force microscopy, ultraviolet–visible–near infrared scanning spectrophotometry, and spectroscopic ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of films. Results show that the film roughness increased with the increase of oxygen pressure, and decreased with the application of OPE. Meanwhile the use of oxygen plasma in a 2 Pa O₂ pressure resulted in the transmittance of the thin film of 91.8% at its peak position (the transmittance of bare substrate). Moreover, the root-mean-square roughness as low as 0.736 nm, and refractive index of 2.18 at 633 nm wavelength, close to the refractive index of bulk Ta₂O₅ (~ 2.20 at 633 nm wavelength), were obtained.     

Electrical properties of Ta2O5 films deposited on ZnO

High dielectric constant (high-k) Ta₂O₅films have been deposited on ZnO/p-Si substrate by microwave plasma at 150°C. Structure and composition of the ZnO/p-Si films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for chemical composition. The electrical properties of the Ta₂O₅/ZnO/p-Si metal insulator semiconductor (MIS) structures were studied using high frequency capacitance-voltage (C-V), conductance-voltage (G-V) and current-voltage (I-V) characteristics. Charged trapping properties have been studied by measuring the gate voltage shift due to trapped charge generation under Fowler-Nordheim (F-N) constant current stressing.     

Fabrication of Ta3N5-Ag nanocomposite thin films with high resistivity and near-zero temperature coefficient of resistance

In this study, we investigate as-deposited Ta₃N₅-Ag nanocomposite thin films with near-zero temperature coefficients of resistance (TCRs) that are fabricated by a reactive co-sputtering method; these films can be used in thin-film embedded resistors. In these films, the TCR approaches zero due to compensation between Ag (+TCR) and Ta-N (−TCR) at resistivities higher than 0.005 Ω-cm.Taking into account the fact that Ag counterbalances the resistivity of the Ta₃N₅-Ag thin film, we performed reactive co-sputtering at a nitrogen partial pressure of 55%, corresponding to a resistivity of 0.384 Ω-cm. The resistivity and power density changed, respectively, from 1.333 Ω-cm and 0.44 W/cm² for silver to 0.0059 Ω-cm and 0.94 W/cm² for the Ta₃N₅-Ag thin film. A near-zero TCR of + 34 ppm/K was obtained at 0.94 W/cm² in the Ta₃N₅-Ag thin film without heat treatment.     

Properties of polyimide/Al2O3 and Si3N4 deposited thin films

Polyimide (PI) nanocomposites with different proportions of Al₂O₃ were prepared via two-step reaction. Silicon nitride (Si₃N₄) was deposited on PI composite films by a RF magnetron sputtering system and used as a gas barrier to investigate the water vapor transmission rate (WVTR). The thermal stability and mechanical properties of a pure PI film can be improved obviously by adding adequate content of Al₂O₃. At lower sputtering pressure (4 mTorr), the PI/Al₂O₃ hybrid film deposited with Si₃N₄ barrier film exhibits denser structure and lower root mean square (RMS) surface roughness (0.494 nm) as well as performs better in preventing the transmission of water vapor. The lowest WVTR value was obtained from the sample, 4 wt.%Al₂O₃-PI hybrid film deposited with Si₃N₄ barrier film with the thickness of 100 nm, before and after bending test. The interface bonding, Al-N and Al-O-Si, was confirmed with the XPS composition-depth profile.     

Effect of working pressure on the properties of BaTiO3-CoFe2O4 composite films deposited on STO (100) by PLD

The BaTiO₃-CoFe₂O₄ (BTO-CFO) composite films were grown on SrTiO₃ (STO) (100) substrates at 750 °C under various working pressures by pulsed laser deposition. The composite film grew into a supersaturated single phase at the working pressure of 10 mTorr, BTO and CFO (00 l) oriented hetero-epitaxial films on STO (100) at 100 mTorr, and a polycrystalline composite film at 500 mTorr. The slow growth rate at high working pressure led to the phase separation in the composite film. The CFO was compressively strained along out-of-plane due to the lattice mismatch with the BTO matrix phase. The BTO-CFO composite film grown at 100 mTorr showed reversible switching of ferroelectric polarization and magnetic hysteresis with strong magnetic anisotropy.