Key Engineering Materials Vol. 388

Abstract: The relationship between the distribution of hydrogen and the electrical properties of (Ba, Sr)TiO3 (BST) thin film capacitors was investigated using secondary ion mass spectroscopy (SIMS) analyses. It has been clearly shown that there is a close relationship between the hydrogen distribution in BST thin film and the frequency dependence of the complex impedance of the BST thin film capacitors. It was confirmed that protons, the interstitial hydrogen impurity dissolved in BST thin films annealed at 400oC, were produced by a thermal equilibrium reaction between the hydrogen in the annealing atmosphere and the BST thin films.

Abstract: Various BaTiO3 thin films were fabricated at 650oC by using different conditions such as the heating rate and alkoxy-derived gel-film thickness. In this study, the spin-coating and calcination step were repeated several times to control the gel-films thickness. And then the one-sintering was carried out with various heating rates. BaTiO3 films with perovskite phase were obtained by using the heating rate of 100oC/sec and the surface morphology became rough with increase of gel-film thickness. We considered that the change of root mean square (rms) roughness and cross-sectional profiles by various heating rates was caused by densification.

Abstract: Effect of annealing temperature on the dielectric properties of Bi1.5Zn1.0Nb1.5O7 films prepared on (111)Pt//(001)Al2O3 and (111)Pt/fused silica substrates by MOCVD was investigated. The tunability and the inverse of the dielectric loss [1/ (tan )] increased with increasing annealing temperature. Relative dielectric constant and temperature coefficient of the capacitance (TCC) increased with the crystallinity of the films. On the other hand, (1/tan ) was independent of the crystallinity of the films, but was dramatically increased by the annealing.

Abstract: Lithium niobate (LiNbO3) thin films were deposited on Al2O3(001) substrates using metal-organic chemical vapor deposition (MOCVD), with Li(dpm) and Nb(C2H5)5 as precursors. By optimizing the conditions of thin film deposition, the c-axis oriented and epitaxially grown LiNbO3 thin films with stoichiometric composition were deposited on an Al2O3(001) substrate. The refractive index of the stoichiometric LiNbO3 thin film was 2.24 at = 632.8 nm, which is close to that of bulk crystal.

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: MBi4Ti4O15 (M=Ba,Ca) thick films were prepared by screen printing and firing using Pt bottom electrodes and ZrO2 substrates. Screen-printable pastes were prepared by kneading the MBi4Ti4O15 powder in a three-roll mill with an organic vehicle. The microstructures and electric properties of the thick films were examined in comparison with bulk ceramics. The remanent polarization of 6.2 9C/cm2 and coercive field of 130kV/cm were obtained for the CaBi4Ti4O15 thick film fired at 1130OC. The Curie points of MBi4Ti4O15 (M=Ba,Ca) thick films from dielectric peaks were 450OC and 790 OC for M=Ba and M= Ca.

Abstract: The (Ba0.6Sr0.4)TiO3 (BST) thin films were formed on a Pt bottom electrode/glazed-Al2O3 substrates by a chemical solution deposition (CSD) method. The BST films were annealed at temperatures between 600 and 800°C in a rapid thermal annealing (RTA) process and grown at each temperature with a random orientation. The grain size of the BST films enlarged and the electrical properties of the BST films improved as the annealing temperature rose. The grain size of the film annealed at 800°C enlarged to be 80 nm. The averaged surface roughness Ra was 2.927 nm, which resulted in a favorable degree of planarity. The dielectric constant and loss tangent of the film at 1 MHz were 403 and 0.049, respectively. The film also displayed a high degree of tunability, which was 58.3% (at 429 kV/cm). These results indicated that high-quality BST thin films could be formed on an extremely cheap glazed-Al2O3 substrates.

Abstract: To retain the driving properties of metal-based micro optical scanner derived by aerosol deposition (AD) technique, CO2 laser irradiation was used to anneal the PZT films deposited onto the stainless-steel substrate. Stainless-steel mirror and frame of the scanner with the film annealed by laser irradiation maintained their metallic luster. The scanner with the film annealed by laser irradiation at 600 °C for 1 min has a scanning angle over 30 degree that is comparable with the scanning angle of a similar scanner annealed by electric furnace at 600 °C for 10 min.

Abstract: The electrical degradation mechanisms of BaTiO3-based ceramics were investigated by measuring the dependence of leakage current on high electric fields. Before the degradation, the leakage current predominately obeyed Ohm’s law and Poole-Frenkel relation. As the degradation progressed, the Poole-Frenkel emission current increased. Moreover, the total current at the high electric fields also comprised Schottky emissions between cathodes and dielectric layers.

Abstract: Magnetic-field-assisted electrophoretic deposition (B-assisted EPD) method has been applied for synthesizing a(b)-axis-oriented Bi5FeTi3O15 ceramics, and the effects of the B-assisted EPD on grain orientation and microstructures have been investigated. The sintering at 1100oC of the green compact obtained by the B-assisted EPD led to dense ceramics with a high relative sintered density of 98%. X-ray diffraction analysis shows that the a(b)-axis-orientation degree of the grain oriented ceramics evaluated by the Lotgering method was 45 %.