Phase stabilization and microstructural studies of lead lanthanum titanate thin films

Thin ferroelectric films of PLTx (Pb_1−xLa_xTi_1−x/4O₃) have been prepared by a sol-gel spin coating process. As deposited films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various concentrations of La (x = 0.04, 0.08 and 0.12) on ITO coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out on films annealed at temperatures (350, 450, 550 and 650 °C). Characterization of these films by X-ray diffraction shows that the films annealed at 650 °C exhibit tetragonal phase with perovskite structure. Atomic force microscope (AFM) images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Fourier transform infrared spectra (FTIR) studies of PLTx thin films (x = 0.08) deposited on Si substrates have been carried out to get more information about the phase stabilization.     

Surface morphology of r.f. sputtered bismuth titanate thin films

Bismuth titanate (Bi₄Ti₃O₁₂) thin films were prepared by the r.f. sputtering technique. A bismuth-rich target was used to compensate for the loss of bismuth during deposition. Studies on many films, deposited under various conditions, showed that existence of non-uniform erosion leads to many surface morphological features. This varying surface structure is a consequence of the resputtering process. Because the microstructure has a significant effect on the films electrical/optical response, a knowledge of its dependency on process parameters is an important step towards device development.     

Preparation and characterization of Ce-doped BaTiO3 thin films by r.f. sputtering

Ce-doped BaTiO₃ thin films prepared on silicon-platinium by r.f. sputtering has been investigated. BaTiO₃ doped with 5.5 mol%CeO₂ thin film was deposited at 550°C substrate temperature in an Ar atmosfere. The crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy with EDAX. Analysis by X-ray diffraction patterns show that the crystalline film with a cubic structure of BaTiO₃, was obtained. The surface morphology (roughness, the grain size and the droplet size) of the thin film surface was examined by atomic force microscopy (AFM). The grain size is about 160 nm, the droplet size is about 0.675 m and the roughness is 36.88 nm. EDAX analysis established a composition of the film to be identical with that of the target (BaTiO₃ doped with 5.5 mol%CeO₂). The broad peak in the capacitance versus temperature curve at the Curie point indicate that the r.f. sputtered Ce-doped BaTiO₃ film is ferroelectric. The values of the capacitance of the thin film at 1 KHz were found to be 86 pF and the loss dielectric was tan = 0.0875. The film exibits a dielectric anomaly peak at 23°C showing ferroelectric to paraelectric phase transition.     

Piezoelectric ZnO films by r.f. sputtering

Piezoelectric zinc oxide films are used in microelectromechanical systems (MEMS) applications, where they can be used in sensors to detect, e.g., pressure or acceleration. Beside sensors, ZnO films are applied in activation devices, where force is needed. Conductive-doped zinc oxide (most often with aluminum) is also used in optoelectronics. Piezoelectric films including AlN and ZnO are more difficult to produce than the corresponding conductive materials. In order to achieve good piezoelectricity in ZnO films, they have to possess high purity, a (0 0 1) orientation (ZnO has hexagonal crystal structure), high resistivity, and fine columnar microstructure perpendicular to the substrate. We have used r.f. magnetron (13.56 MHz) sputtering from a ZnO target in an oxygen atmosphere to achieve the piezoelectric ZnO. The aim of this work has been to develop an r.f. sputtering process for ZnO to achieve highly piezoelectric thin films. As a test vehicle to measure the piezoelectricity of the ZnO films we have fabricated resonators and passband filters in the 1–2 GHz range using standard microelectronics photolithography, deposition, and etching techniques on 100-mm diameter Corning glass or silicon wafers. The influence of the sputtering-process parameters on the film properties has been studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, and electrical measurements. In this study, the effects of the process parameters on the final material properties of the ZnO film are discussed in detail.     

Effect of post-deposition annealing on microstructural and optical properties of barium strontium titanate thin films deposited by r.f. magnetron sputtering

The effect of post-deposition annealing on the structural and optical properties of barium strontium titanate, Ba_0.8Sr_0.2TiO₃ film has been investigated. The films have been deposited on oxidized p-silicon substrates by r.f. magnetron sputtering followed by annealing in O₂ atmosphere at different temperatures. In situ deposition has also been carried out at 550 °C for comparison. The nature of the variation of refractive index and extinction coefficient with annealing temperature and wavelength has been studied. Absorption band edges shift towards lower photon energy values as the temperature is increased causing a reduction in the optical band gap energy. Infrared absorption bands show a cubic symmetry at lower frequency and are found to be broadened and even split at higher frequency.     

Phase formation and characteristics of r.f.-sputtered barium-strontium titanate thin films on various bottom layers

(Ba_0.7Sr_0.3)TiO₃ thin films were deposited by r.f.-magnetron sputtering on Pt/Ti/Si, Pt/TiSi₂/Si and Pt/Ti/SiO₂/Si substrates, respectively, and annealed at 650 C for 30s by Rapid Thermal Annealing (RTA). XRD (X-ray diffraction) patterns revealed that the BST films had perovskite structure without preferred orientation. Auger depth profiles of barium-strontium titanate (BST) films on various substrates were performed. In the Pt/Ti/Si and Pt/TiSi₂/Si structures, Si diffused into the BST film, but in the Pt/Ti/SiO₂/Si structure, the diffusion of Si into the BST film was prevented and the interface between the BST film and the electrode was stable. The dielectric constants were about 310–260 (100 kHz–1 MHz).     

Preparation of Fe-N films by r.f. sputtering

Fe-N films over a wide compositional range have been prepared by the reactive sputtering method. Fe-N sputtered films were composed of a single or two phases such as-Fe₂N,-Fe_3.02N,-Fe_3.82N,-Fe₄N and-Fe; however, an unknown phase was observed at a higher nitrogen pressure. A remarkable preferred orientation of the-Fe_3.02N (110) plane parallel to the film surface was observed. The Curie temperature of the sputtered -Fe_3.82N sample was 490° C, which was almost the same as that of-Fe₄N prepared by metal nitriding. The saturation magnetization, _s, of the sputtered Fe-N samples decreased from 151.8 to 42.4 e.m.u.g^–1 with increasing nitrogen content from 7.94 to 24.87 at%, and its coercive force,₁ H _c was found to lie in the range 150 to 600 Oe in the powder form at room temperature.     

Combinatorial deposition of EL phosphor thin films by r.f. magnetron sputtering using a subdivided powder target

A new technique incorporating combinatorial deposition by r.f. magnetron sputtering was used to develop new Eu-activated multicomponent oxynitride thin-film phosphors for electroluminescence. By sputtering with a powder target that is subdivided into two parts, phosphor thin films with a chemical composition that varied across the substrate surface could be successfully prepared. Thin-film electroluminescent (TFEL) devices were fabricated incorporating various Eu-activated phosphor host materials such as multicomponent oxynitrides: GaN, AlN or Si₃N₄ combined with Ga₂O₃, CaO or ZnO. In ((AlN)_1−X–(CaO)_X):Eu thin films, for example, the chemical composition (CaO content (X)) could be optimized to obtain higher electroluminescent and photoluminescent emission intensities by using only one deposition with the new technique. As a result, a luminance of 170 cd/m² for red emission was obtained in an ((AlN)_0.1–(CaO)_0.9):Eu TFEL device driven at 1 kHz. High luminances were also obtained in red-emitting-TFEL devices using either a ((GaN)_0.9–(Ga₂O₃)_0.1):Eu or a ((GaN)_0.8–(ZnO)_0.2):Eu thin film prepared with an optimized composition.     

Reactive ion beam sputtering of thin films of lead,zirconium and titanium

Thin films of lead, zirconium and titanium were reactively sputtered in an oxygen atmosphere by a focused ion beam sputtering technique. With this technique, the plasma is contained in the ion gun so that neither the target nor the substrate is in a plasma environment. As a result, several factors which can interfere with the interpretation of the mechanism of compound formation (high energy secondary electron bombardment, high substrate temperature, high deposition pressure) are virtually eliminated.Properties such as deposition rate, resistivity and internal stress as a function of the partial pressure of oxygen were investigated. A decrease in the deposition rate was observed as the partial pressure of oxygen was increased from 1 × 10^-6 to 2 × 10^-4 Torr. This decrease was attributed to a build-up of a surface layer of adsorbed oxygen on the target. A model is proposed to predict the partial pressure of oxygen at which a dielectric film forms, based on the thermodynamic properties of the compound formed. All films deposited are in tensile stress. This suggests that compound formation occurs at the target and that the oxide is sputtered in the collision process.     

On the properties of AlN thin films grown by low temperature reactive r.f. sputtering

In this paper we report on the growth of c-axis-oriented AlN thin films by low temperature reactive r.f. sputtering and the results of their examination and analysis in a variety of ways. In addition to using other substrates, we fabricated c-axis- oriented AlN films on aluminium film substrates. A hexagonal column structure was observed in the morphology of replicas of the natural surfaces of films. As well as the dielectric constant ε, the resistivity ϱ, the breakdown field E_p and the refractive index n, curves of ε versus frequency f, ε versus temperature T and conductivity σ versus T were measured. The IR absorption spectrum of an AlN film sputtered at low temperature coincides with that of an AlN film sputtered onto a high temperature substrate and of a bulk crystal, which remains unchanged after annealing. The band gap E_g = 5.9–6.0 eV, which remains unchanged after annealing in N₂ at 900°C. Theoretical calculation of the dispersion curve of surface acoustic waves by an AlN/glass structure shows that the curve is very level in the range hk = 0.2–0.6. The capacitance-voltage curve of an Al/AlN/Si structure is given in this paper.     

射频磁控溅射制备TiO2-xNx薄膜及其光催化特性研究

利用射频磁控溅射在玻璃衬底上制备了透明TiO2 和 TiO2-x Nx 薄膜样品,通过 X 射线衍射(XRD)、原子力显微镜(AFM)及 UV Vis分光光度计等测试手段表征了样品的结构、形貌和光催化性能。结果表明制备的薄膜为锐钛矿相结构。随着 N2/Ar气流比的增大薄膜样品出现新的物相,吸收光谱向可见光方向展宽,在N2/Ar流量比为 3∶100 时,制备的薄膜在可见光区具有很好的光催化性能。     

Improved dielectric properties of lead lanthanum zirconate titanate thin films on copper substrates

Thin films of lead lanthanum zirconate titanate (PLZT) were directly deposited on copper substrates by chemical solution deposition and crystallized at temperatures of ~ 650 °C under low oxygen partial pressure (pO₂) to create film-on-foil capacitor sheets. The dielectric properties of the capacitors formed have much improved dielectric properties compared to those reported previously. The key to the enhanced properties is a reduction in the time that the film is exposed to lower pO₂ by employing a direct insertion strategy to crystallize the films together with the solution chemistry employed. Films exhibited well-saturated hysteresis loops with remanent polarization of ~ 20 μC/cm², dielectric constant of > 1100, and dielectric loss of < 0.07. Energy densities of ~ 32 J/cm³ were obtained at a field of ~ 1.9 MV/cm on a ~ 1 μm thick film with 250 μm Pt electrodes.     

D.c. properties of ZnO thin films prepared by r.f. magnetron sputtering

In the development of ZnO-based varistors the electrical properties of ZnO/Bi₂O₃ junctions and of the two individual oxides are being investigated. Following our recent work on a.c. conductivity in Al---ZnO---Al sandwich structures we currently report d.c. measurements. The structures were prepared by r.f. magnetron sputtering in an argon/oxygen mixture in the ratio 4:1. Capacitance-voltage data confirm that the Al/ZnO interface does not form a Schottky barrier and measurements of the dependence of capacitance on film thickness indicate that the relative permittivity of the films is approximately 9.7. With increasing voltage the current density changed from an ohmic to a power-law dependence with exponent n≈3. Furthermore measurements of current density as a function of reciprocal temperature showed a linear dependence above about 240 K, with a very low activation energy below this temperature consistent with a hopping process. The higher temperature results may be explained assuming a room-temperature electron concentration n₀ and space-charge-limited conductivity, dominated by traps exponentially distributed with energy E below the conduction band edge according to N = N₀exp(−E/kT_t), where k is Boltzmann's constant. Typical derived values of these parameters are: n₀ = 7.2 × 10¹⁶ m⁻³, N₀ = 1.31 × 10⁴⁵ J⁻¹ m⁻³ and T_t = 623 K. The total trap concentration and the electron mobility were estimated to be 1.13 × 10²⁵ m⁻³ and (5.7−13.1) ×10⁻³m²V⁻¹s⁻¹ respectively.     

Voltaic cells of (ZnxCuy)Oz thin films deposited by r.f. sputtering

The growth of (Zn₂₈₋₄₂Cu₃₉₋₂₅)O₃₃ thin films deposited by r.f. sputtering was studied. Voltaic elements with an ITO/(Zn, Cu)O/Al structure (where ITO is indium tin oxide) were fabricated. The open-circuit voltage and short-circuit current at temperatures of 0–45 °C were 0.5–1.25 V and 0.3–1.5 μA cm^-2 respectively. The composition of the films was studied by Auger analysis.     

Structural properties of TiO2–WO3 thin films prepared by r.f. sputtering

TiO₂–WO₃ thin films were prepared by radio frequency (r.f.) reactive sputtering from metallic target. Structural and morphological properties of the thin films have been studied through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The influence of the annealing on the phase composition TiO₂–WO₃ system was studied. The binding energies of titanium and tungsten are characteristic for Ti⁴⁺ and W⁶⁺. The influence of tungsten on anatase–rutile phase transition in TiO₂ was observed. The structural modeling has been performed to account the preferred orientation in tungsten doped titanium oxide.