Fabrication and electrical properties of Ba0.64Sr0.36TiO3 thin films by sol-gel on platinum coated silicon

The Ba_0.64Sr_0.36TiO₃ thin films have been prepared by the sol-gel method on a platinum-coated silicon substrate. The structure and electrical properties of sol-gel derived Barium-strontium-titanate (Ba_0.64Sr_0.36TiO₃) thin films have been investigated. The as-fired thin films are found to be amorphous, and the films crystallize to a perovskite structure after a post deposition annealing at 700°C for 1 h in air. The dielectric constant and dissipation factor for Ba_0.64Sr_0.36TiO₃ thin film at a frequency of 200 Hz were 592 and 0.028, respectively. The temperature dependence of dielectric constant and dissipation factor exhibited a diffused ferroelectric to paraelectric phase transition at 40°C. The ferroelectric nature of this film at room temperature was confirmed by the existence of butterfly-shaped C-V curves caused by switching of the ferroelectric domains. The capacitance changed from 495 to 1108 pF with the applied voltage in the –5 to +5 V range at a frequency of 100 kHz. The pyroelectric coefficient at room temperature (25°C) is 1860 C/m²K, and the figure-of-merit of this film is 37.4 C/m³K. The high pyroelectric coefficients and the greater figures of merit of Ba_0.64Sr_0.36TiO₃ thin films make it possible to be used for thermal infra-red detection and imaging.     

Structural and pyroelectric properties of sol–gel derived multiferroic BFO thin films

Multiferroic BFO/PZT multilayer films were fabricated by spin-coating method on the (1 1 1)Pt/Ti/SiO₂/Si substrate alternately using PZT(30/70), PZT(70/30) and BFO alkoxide solutions. The structural and ferroelectric properties were investigated for uncooled infrared detector applications. The coating and heating procedure was repeated six times to form BFO/PZT multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without presence of the second phase such as Bi₂Fe₄O₃. The thickness of BFO/PZT multilayer film was about 200–220 nm. The ferroelectric properties such as dielectric constant, remnant polarization and pyroelectric coefficient were superior to those of single composition BFO film, and those values for BFO/PZT(70/30) multilayer film were 288, 15.7 μC/cm² and 9.1 × 10^?9 C/cm² K at room temperature, respectively. Leakage current density of the BFO/PZT(30/70) multilayer film was 3.3 × 10^?9 A/cm² at 150 kV/cm. The figures of merit, F_V for the voltage responsivity and F_D for the specific detectivity, of the BFO/PZT(70/30) multilayer film were 6.17 × 10^?11 Ccm/J and 6.45 × 10^?9 Ccm/J, respectively.     

Giant pyroelectric coefficient of Mn-doped PLT thin films epitaxially grown on (001) Pt/MgO

The c-axis-oriented epitaxial thin films of Mn-doped Pb_1−xLa_xTi_1−x/4O₃ (PLT) on (001) Pt/MgO substrates were prepared by rf-magnetron sputtering. To investigate the effect of the doped ion, 0-1.7 mol% MnO₂ added to the PLT target powder. The temperature dependence of the relative dielectric constant ?_r measurements and modified Curie-Weiss plots suggested that the increasing of diffuseness n was induced by high-La substitution and the diffuseness n of PLT thin films decreased by the addition of Mn, considerably. Inner stress and thermodynamic analysis were carried out and the results propose that the increasing of γ with Mn doping caused by increasing the misfit strain of the c-axis-oriented epitaxial PLT thin films and substrate. As a result, giant pyroelectric coefficient (γ = 15.8 × 10⁻⁸ C/cm² K) of Mn-doped epitaxial PLT thin film was achieved.     

In-situ deposition of superconducting YBCO thin films by magnetron sputtering from powder target

We have used stoichiometric Y₁Ba₂Cu₃O_7–x powder as magnetron sputtering target to deposit high-quality high-T _c superconducting thin films on MgO, SrTiO₃, and ZrO₂ substrates. The zero-resistance temperatures are 86–88 K, and the 77 K zero-field critical current density is 8 × 10⁵ A/cm². The films are highlyc-axis oriented. Films deposited on 10 × 10 × 1 mm³ ZrO₂ substrates have surface resistances below 25 m at 77 K and 94 GHz. Using powder targets instead of bulk targets has the following advantages: simple and low-cost target preparation, simple target replacement, and versatility for large-area deposition.     

Pyroelectric Ta-modified LiNbO3 thin films and devices for thermal infrared detection

High-performance pyroelectric infrared (IR) detectors have been fabricated using tantalate-doped lithium niobate LiNb_1 − xTa_xO₃ (abbreviated as LNT, with x = 0-1.0) thin films deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by diol-based sol-gel processing, in which, tantalate (Ta) is adopted as dopant in lithium niobate. The randomly oriented LNT thin film exhibits a relatively small dielectric constant and a large pyroelectric coefficient. The pyroelectric characteristics of detectors with various tantalate contents, as a function of modulation frequency, were investigated. It was found that LiNb_0.8Ta_0.2O₃ had the largest voltage responsivity of 7020 (V/W) at 70 Hz, and a specific detectivity (D^?) of 7.76 × 10⁷ cm Hz^1/2/W at 200 Hz. These results indicate that the LNT thin film with x = 0.20 is most suitable for application as high-performance pyroelectric thin-film detectors.     

Preparation and electrical properties of ITO thin films by dip-coating process

Indium tin oxide (ITO) thin films were prepared on quartz glass substrates by a dip-coating process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. The ITO thin films containing 0 20 mol% SnO₂ were successfully prepared by heat-treatment at above 400 °C. Chemical stability of sol were investigated by using a FTIR spectrometer. The electrical resistivity of the thin films decreased with increasing heat-treatment temperature, that is carrier concentration increased, and mobility decreased with increasing SnO₂ content. The ITO thin films containing 12 mol% SnO₂ showed the minimum resistivity of =1.2 × 10^–3 ( cm). It also showed high carrier concentration of N=1.2 × 10²⁰(cm^–3) and mobility _H=7.0(cm² V^–1 s^–1).     

Dielectric and pyroelectric properties of KNO3 thin-layers

A series of thin monocrystalline KNO₃ layers has been grown from the melt by a special technique. The changes of the dielectric constant, d.c. resistivity, activation energy and pyro-electric current behaviour with the layer thickness and temperature have been investigated. Also, the effect of the a.c. frequency on the dielectric constant is checked in the frequency range 1 to 10 kHz. A sharp drop in dielectric constant could be recorded up to 6 kHz. The layers exhibit essentially the same dielectric and pyroelectric properties as bulk KNO₃ single crystals. The various measured parameters of these layers were found to be thickness-dependent. TheI-V characteristics of the layers (5m thickness) reveal the presence of breakdown voltage at 10.95V. Maximum pyrocurrent was obtained at positive d.c. biasing voltage. Also, the layers show a high pyroelectric coefficient, e.g. for layer thickness 8.9m, = 60C cm^–2 K^–1 at 180° C. The study proved that thin layers of potassium nitrate have good pyroelectric properties and should be useful as pyroelectric thermal detector material.     

Structural,electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique

A low cost chemical bath deposition (CBD) technique has been used for the preparation of Cu_2–xSe thin films on glass substrates. Structural, electrical and optical properties of these films were investigated. X-ray diffraction (XRD) study of the Cu_2–xSe films annealed at 523 K suggests a cubic structure with a lattice constant of 5.697 Å. Chemical composition was investigated by X-ray photoelectron spectroscopy (XPS). It reveals that absorbed oxygen in the film decreases remarkably on annealing above 423 K. The Cu/Se ratio was observed to be the same in as-deposited and annealed films. Both as-deposited and annealed films show very low resistivity in the range of (0.04–0.15) × 10^–5 -m. Transmittance and Reflectance were found in the range of 5–50% and 2–20% respectively. Optical absorption of the films results from free carrier absorption in the near infrared region with absorption coefficient of 10⁸ m^–1. The band gap for direct transition, E_g.dir varies in the range of 2.0–2.3 eV and that for indirect transition E_g.indir is in the range of 1.25–1.5 eV.     

Measurement of the surface resistance of YBa2Cu3O7?x thin films using stripline resonators

We review methods of measuring surface resistance (R _s ) of thin films using stripline resonators, and present our measurements of theR _s of YBa₂Cu₃O_7–x films as a function of frequency, temperature, and r.f. magnetic field. The films were deposited on LaAlO₃ substrates by two methods: (1) electron-beam coevaporation of Y, BaF, and Cu followed by annealing in O₂, and (2) single-targetin situ sputtering. The measurements were obtained at frequencies from 0.4 to 10 GHz, temperatures from 4 to 90 K, and an r.f. magnetic field range from 0 to 30 Oe. At low temperature and low r.f. field at 0.4 GHz, theR _s values obtained for the two deposition methods are approximately 7×10^–6 and 4×10^–6 , respectively.     

Reduction of dislocation density in GaN films on sapphire using AIN interlayers

GaN (00.1) thin films, of thickness 1.25 to 2.25 m grown on sapphire substrate (11.0) by metallo organic chemical vapor phase deposition (MOCVD) with different number of AlN interlayers, were characterized by triple crystal diffractometry and synchrotron white beam x-ray topography (SWBXT). The full width at half maximum (FWHM) of x-ray rocking curves from symmetric and asymmetric reflections was used to estimate the dislocation density in GaN films. It has been found that the edge dislocation density decreased from 1.63 × 10¹⁰ cm^–2 to 1.23 × 10¹⁰ cm^–2 and the screw dislocation density decreased from 2.0 × 10⁸ cm^–2 to 1.1 × 10⁸ cm^–2 when one AlN interlayer was inserted between the high temperature GaN layer. The dislocation density decreased further with the increase in number of interlayers. On the other hand the compressive stress in the GaN film increased from –0.29 GPa to –0.86 GPa. The compressive stress further increased as the number of interlayers increased but no cracking in the GaN film was observed. This could be due to better adhesion between the film and substrate due to interlayers. SWBXT in transmission from a GaN(00.1)/Al₂O₃(11.0) sample confirms the orientation of GaN and indicates that it is a single crystal with high dislocation density. SWBXT from the Al₂O₃ substrate shows cellular structure of dislocations.     

Bias voltage dependence properties of cadmium oxide films deposited by d.c. reactive magnetron sputtering

Cadmium oxide films were grown on glass substrates using d.c. reactive magnetron sputtering technique by sputtering from a metallic cadmium target in an oxygen partial pressure of 1×10^–3 mbar under various substrate bias voltages. The substrate bias voltage significantly influences the crystallographic structure of the deposited films. The influence of substrate bias voltage on the electrical and optical properties of the films was systematically studied. The films formed at a substrate temperature of 473 K and bias voltage of –80 V showed an electrical resistivity of 1×10^–3 cm, optical transmittance of 86%, optical band gap of 2.47 eV and a figure of merit of 7×10^{–3 –1}.     

Polyaniline films deposited by anodic polymerization: Properties and applications to chemical sensing

Polyaniline conductive thin films have been used for the detection of a number of important gases and vapors: organic solvents, ammonia, oxygen, hydrogen sulfide, nitrogen and sulfur oxides. The films can be produced by spin coating, thermal evaporation, the Langmuir–Blodgett technique and cyclic voltammetry. This paper presents preliminary results on acidity sensing with electrodeposited polyaniline layers. Polyaniline conductive thin films were prepared by anodic polymerization from an acidic solution of the monomer on two kinds of substrates: gold plated silicon and indium-tin oxide on glass. Ultraviolet-visible (UV-VIS) spectrometry of layers showed a maximum absorption peak around 800 nm for all the samples investigated (independent of preparation conditions) and revealed that the polymeric films were in the emeraldine base form, 18–25% protonated. The room-temperature in-plane d.c. conductivities of the polymer films were found to be between 4×10^–9 S cm^–1 and 9×10^–10 S cm^–1 (deposition rate approximately 4 m h^–1; film thickness 750–1100 nm). Immersion of the polyaniline films in dilute hydrochloric solution resulted in changes in the d.c. conductivity by up to nine orders of magnitude, reaching a value of 4×10^–2 S cm^–1 while immersed in the acidic solution. Humidity tests carried out by exposing polyaniline samples to water vapors changed the d.c. conductivity by one order of magnitude to 1.34×10^–8 S cm^–1.     

Preparation and characterization of YBa2Cu3O7?x samples for microwave applications

We prepared several samples of YBa₂Cu₃O_7–x thick films electrophoretically deposited on metallic substrates, thin films sputtered on dielectric substrates, and bulk pellets, and we tested their microwave properties. Various preparation techniques are described in detail and the importance of appropriate thermal treatment during the fabrication process is emphasized. Experimental results show that electrophoretically deposited thick films on silver substrates reached, after heat treatment, a surface resistance at 50 K of 4×10^–2 comparable with the silver value, while the same measurement before sinterization gave a value of 0.5 . Either bulk pellets or thin films gave worse results, though a lack of sensitivity in our experimental apparatus could have influenced our data. The problem of sensitivity in the characterization of microwave properties of small samples is discussed in the appendices.     

Chemical Vapor Deposition of Copper Films from Copper Dipivaloylmethanate in Hydrogen Atmosphere

Data are presented on the kinetics and mechanism of copper deposition from Cu(dpm)₂ vapor in a hydrogen atmosphere at normal pressure. From kinetic analysis of the deposition rate as a function of substrate temperature (200–390°C) and Cu(dpm)₂ vapor pressure (7.8 Pa), the main parameters of kinetically limited deposition were determined: activation energy of 27 ± 7 kJ/mol, preexponential factor of (2.9 ± 1.8) × 10² cm/s, and reaction order of unity. Under diffusion-control conditions, the diffusion rate constant is 4.8 cm/s, and the thickness of the diffusion layer is 8 × 10^–2 cm. The films grow by a mixed (island–layer) mechanism, and their electrical resistivity is close to that of bulk copper.     

Preparation and characterization of radio-frequency-sputtered Ba2Si2TiO8 thin films

Radio-frequency-sputtered barium titanium silicate (BST, Ba₂Si₂TiO₈) thin films were grown on crystalline Si (100) substrates and were characterized using wavelength-dispersive spectrometry (WDS), X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), and diagonal techniques for dielectric properties. The chemical compositions of the films increasingly deviated from stoichiometry with film thickness. At the initial stage of deposition the grain configuration is dependent on the Si substrate texture. XRD analysis indicates that the BST films deposited at an optimum substrate temperature of 845 °C were strongly c-axis oriented, and that the film orientation is manipulated by substrate temperature and supersaturation. The corresponding film-growth rate in the direction normal to the film surface at 845 °C was 1.95 nm min^–1 at the initial stage, and decreased with sputtering time. The as-deposited films have a room-temperature bulk resistivity of 1.8 ×10⁷ m in the direction of thickness and an isotropic surface resistivity of 1.5×10³ m. The high-frequency relative dielectric constant, 0.05 at frequencies higher than 9 MHz, is lower than that of many typical piezoelectric materials. The high-frequency impedance character is typical of piezoelectric materials, giving a minimum impedance frequency of 9.0 MHz and a serial resonant frequency at about 9.5 MHz.     

Laser annealing of Pb(Zr0.52Ti0.48)O3 thin films for the pyroelectric detectors

Lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃, PZT) thin films fabricated by magnetron sputtering technique on the Pt/Ti/SiO₂/Si substrates at room temperature, were annealed by means of CO₂ laser with resulting average substrate temperature below 500 °C. The crystal structure, surface morphology and pyroelectric properties of the PZT films before and after annealing were investigated by X-ray diffraction, atomic force microscopy, and pyroelectric measurements. The results show that the annealed PZT thin film with a laser energy density of 490 W/cm² for 25 s has a typical perovskite phase, uniform crystalline particles with a size of about 90 nm, and a high pyroelectric coefficient with 1.15 × 10^− 8 Ccm^− 2 K^− 1.     

Effect of TiOx seed layer on the texture and electric properties in La and Ca modified PbTiO3 thin films

Lanthanum-and calcium-modified PbTiO₃ (PLCT) ferroelectric thin films were successfully prepared on Pt(111)/Ti/SiO₂/Si substrates by pulsed laser deposition. Influence of TiO_x seed layer on texture and electric properties of PLCT films was investigated. It is found the PLCT films without seed layer exhibited highly (100)-textured, while using about 9 nm TiO_x as seed layer lead to highly (301)-textured. The PLCT film with TiO_x seed layer possess higher remnant polarization (Pr = 26 µC/cm²), better pyroelectric coefficient and figure of merit at room temperature (p = 370 µC/m²k, F_d = 190 × 10^− 5 Pa^− 1/2) than that of film without seed layer. The mechanism of the enhanced electric properties was also discussed.     

Correlation Between the Morphology of Ag and the Contact Resistivity of the Ag/YBa2Cu3O7?δ Thin Film Contact

The morphology of the silver films deposited and annealed on laser ablated YBa₂Cu₃O_7– thin films and the corresponding contact resistivity have been systematically investigated. A minimum contact resistivity of 6 × 10^–8 cm² was reached at 77 K by annealing Ag/YBa₂Cu₃O_7– contact at the optimum temperature. The effect of the annealing temperature on the contact resistivity was explained by considering the morphology of the silver films and the diffusion of silver into YBa₂Cu₃O_7– film, etc. The difference of the contact resistivity for Ag contact to polycrystalline, single crystal and thin film of YBa₂Cu₃O_7– were also explained.     

Nucleation control of diamond synthesized by microwave plasma CVD on cemented carbide substrate

Diamond was coated on to cemented carbide substrate by microwave plasma CVD, in which nucleation control of diamond crystals was investigated under constant deposition conditions; total pressure 30 torr, CH₄ flow rate 1 ml min^–1, H₂ flow rate 199 ml min^–1 and microwave power 550 W. Nucleation tends to occur selectively on the edge part of WC grains of the cemented carbide substrate with coarse WC grain size of about 1 m, where the nucleation density was 9×10⁶ cm^–2. The density increased to about 5×10⁷ cm^–2 when using a finegrained substrate (WC grain size 0.5 m). A considerably enhanced nucleation was observed by introducing a number of fine microflaws on to the substrate surface. Microflawing treatment with diamond fine powder (grain size 0–1/4 m) suspended in an ultrasonic cleaner bath was effective for increasing the diamond nucleation density up to 5×10⁸ cm^–2. The grain size of grown diamond crystals decreased with increasing microflawing time.