Papers by Keyword: BST

Abstract: Ba0.6Sr0.4TiO3 materials doped with boron family Al3+, Ga3+ and In3+ are prepared by a ceramic process. The specimens possess condense microstructures. A low dielectric loss is achieved in the sample doped with In3+. Dielectric constants increase with decrease of the radii of doped ions. The results are discussed with respect to the interaction between oxygen ions and ions at B-site in ABO3 perovskite, which is revealed by Fourier transform infrared spectrum.

Abstract: (Ba,Sr)TiO3 (BST) thin films have been investigated because of significant interest in device applications of their nonlinear dielectric properties such as in frequency tunable devices. We have investigated frequency conversion devices using BST films as new nonlinear devices, such as frequency mixers and multipliers. In this paper, we report the evaluation of nonlinear properties of various capacitors, and the experimental equation of the properties and the equivalent circuit model for frequency converters were established. A frequency multiplier using the BST film capacitor was fabricated, and obvious third harmonic signals could be observed. A conversion efficiency of -20 dB was obtained with a low input power of 0.25 W. Analysis of the converter with an equivalent circuit was also carried out, and the calculated output voltage agreed well with the measured result. The model is expected to be used for the analysis and improvement of conversion devices.

Abstract: (Ba0.6,Sr0.4)TiO3 thick films have been fabricated on various substrates and their physical and electrical properties were analyzed. The effect of primary powder condition on the quality of the BST fabricated films using aerosol deposition technique has been investigated keeping in mind results shown in the literature for BST films fabricated with classical deposition techniques. Presence of carbonates and TiO2 has been demonstrated by XPS analysis and the leakage current behavior has linked to the presence of TiO2 at the grain boundaries. The films showed good insulating properties, with small leakage densities being on the order of 10-6 A/cm2 for an applied electric field of 150 kV/cm.

Abstract: Ba0.6Sr0.4TiO3 (BST) thin films deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering and crystallized by rapid thermal annealing (RTA) exhibit much thinner BST/Pt interfacial transition layer and higher dielectric properties than the films crystallized by conventional thermal annealing (CTA). HRTEM observations show that the transition layer is 2-3nm thick for RTA and 4-5nm thick for CTA. XPS investigations display that the transition layer is composed of perovskited BST phase and non-perovskited BST phase, and RTA corresponds to much less non-perovskited BST phase than CTA. The reason for non-perovskited BST phase and the dielectric properties of BST films are also presented.

Abstract: The effects of cerium oxide on the dielectric properties and tunable properties of barium strontium titanate/magnesia (40wt%Ba0.6Sr0.4TiO3-60wt%MgO) compound ferroelectric material for improving the properties of phase shifter were investigated. The mechanism was also presented and discussed. The XRD patterns analysis showed that with increasing quantities of cerium oxide x (wt%), the lattice constant of BST-MgO material first increased to x=0.4, then changed a little till x=1.2. Further additions of CeO2 decreased the lattice constant. The dielectric properties at 10 kHz and microwave frequency were studied. The addition of CeO2 influences the dielectric constant, loss tangent and tunability greatly. The permittivity decreased with increase of cerium oxide nearly linearly. The addition of CeO2 effectively decreased the loss in BSTM ceramic. Optimum doping amount of CeO2 reduced the high frequency loss tangents of BST-MgO compound which also ensured the moderate dielectric constant and tunability. When the doping amount of CeO2 is 1.2wt%, BST-MgO composite has the following properties: εr = 92.64, tanδ = 0.00449 (at 2.6166 GHz) and tunability = 9.67% (at 2kV/mm), it is suitable for ferroelectric phase shifter.

Abstract: Barium strontium titanate (BST) ferroelectric thin films have been successfully prepared on the single crystal silicon substrates using hydrothermal crystallization of sol-gel precursor, which combined the conventional sol-gel process and the hydrothermal method. The precursor film was deposited by the dip-coating method. The multiplayer BST gel films were hydrothermally treated in a Teflon vessel at low temperature of 160-180 °C for 1-3.5 h. The influences of the reaction conditions on the structure and crystallizing degree of BST thin films were discussed. We find that the temperature of as-dried gel films and post hydrothermal treatment are the critical parameters determining the quality of formation of BST thin films. Under optimized conditions, we can obtain well-developed perovskite BST films with smooth and pinhole-free surfaces. These results reveal that this technique is a promising low temperature process for the fabricating of thin films.

Abstract: BST/PLT composite thick films with various content of PbO-B2O3 glass additive from 5mol% to 25mol% were successfully prepared by screen-printing the paste onto alumina substrates. XRD, SEM and impedance meter were used to analyze the phase structures, morphologies and dielectric properties of the thick films. The results showed that the BST phase has no interaction with PbO-B2O3 glass in the composite thick films at 750 oC. Diffusion between PLT phase and PbO-B2O3 glass phase occurs and the c axis of PLT phase in thick films reduces slightly. The high infiltration between the glass phase and particles densify the composite thick films and the uniform microstructure can be obtained in the thick films with PbO-B2O3 glass additive content of 10mol%. Good temperature stability of dielectric properties is achieved with the 25mol% content of PbO-B2O3 glass additive and the variance of the relative dielectric constant in the temperature range between 0oC and 300oC is 15%.

Abstract: Technology aspects and characterization of BaxSr1-xTiO3 (BST) films fabricated with low pressure plasma jet technique are presented. BST films were deposited on silicon coated with Pt/TiO2/SiO2 and on bare Si substrates. The nozzles-type RF hollow cathode has been fabricated from hot pressed BaTiO3, SrTiO3, and BST ceramics. Controlling of RF voltage, RF current and substrate temperature allowed us to deposit reproducible films with controlled grain size. Hysteresis loops, ellipsometric and micro-Raman investigation results are presented and discussed.

Abstract: Pb0.65Ba0.35ZrO3 (PBZ) thin films have been grown on MgO (001) substrates by pulsed-laser deposition (PLD). We have compared the structural and dielectric properties of PBZ films grown at various temperatures. A highly c-axis orientation has appeared at PBZ film grown at the deposition temperature of 550oC. The c-axis oriented PBZ film has also shown the largest tunability among all the PBZ films in capacitance-voltage measurements. The tunability and dielectric loss of the PBZ film was 20% and 0.00959, respectively. In addition, we have compared the temperature coefficient of capacitance (TCC) of a PBZ film with that of a Ba0.5Sr0.5TiO3 (BST) film which is a well-known material applicable to tunable microwave devices. We have confirmed that TCC value of a PBZ thin film was three-times smaller than that of a BST thin film.