Abstract: We proposed a new type of multi-ferroic system using magnetoelectric (ME:Cr2O3) material/ultra-thin ferroelectric materials (FE)/a magnetoelectric material hetero structure. This ME and FE heterosystem showed a general Polarization – Electric field hysteresis curve. When a magnetic and electric field (ME field) was applied at the same time, a decrease of polarization was observed. This might be due to the antiferromagnetic domain alignment of Cr2O3 by the ME field.
Abstract: Thin films of a bismuth layer-structured dielectric oxides (BLSD), SrBi4Ti4O15, with preferential crystal orientation were prepared by means of chemical solution deposition (CSD) technique on (111)Pt/(100)Si substrate with bottom nucleation layers of conductive perovskite oxides, LaNiO3 and SrRuO3. CSD technique was utilized for the film preparation of SrBi4Ti4O15. These films possessed highly crystal orientation of (00l) BLSD planes parallel to the substrate surface. The leakage current densities of the SrBi4Ti4O15 films on (100)SrRuO3//(100)LaNiO3/(111)Pt/Ti/(100)Si and on (100)LaNiO3/(111)Pt/Ti/(100)Si were approximately 10-6 and 10-7 A/cm2 respectively. The dielectric constants of these films in a frequency range of 102 - 106 Hz were from 310 to 350 and 250 to 260 respectively. The value of capacitance change of these films in the range from 20 to 300 oC was about +8 and +5% respectively.
Abstract: The transparency and uniformity of thin films of titanium oxide (TiO2) are important factors in determining the characteristics of photocatalysts and dye-sensitized solar cells. Synthesized TiO2 nanoparticles were deposited by constant-current electrophoresis deposition in ion-free water and ethanol. The number of cracks was reduced when ethanol was used instead of water. TiO2 nanoparticle thin films produced using a short deposition time had no apparent cracks and a high optical transparency. Moreover, thick TiO2 nanoparticle thin films, which have high optical trans-parency and no apparent cracks, could be deposited by repeating short-time deposition in ethanol.
Abstract: We investigated an influence of interface layer on a tunability of parallel plate (Ba, Sr)TiO3 thin film capacitors. BST thin film capacitors with top electrode of Pt, Au and Ag were fabricated. BST films had thickness of 40, 60, 80 and 120nm. The tunability increased with increasing the BST film thickness. Considering the interfaces between BST films and electrodes as Schottky junctions, depletion layers were formed in the interfaces depending on the difference of the work function of metal electrodes. Larger external bias voltages were applied to the depletion layer than interior BST film, because the permittivity in the depletion layer was smaller than that in interior BST film. Therefore, the depletion layer lowered the tunability. Tunability decreased with increasing the thickness of the depletion layers.
Abstract: The switching behavior of the ferroelectric polarization of magnetoferroelectric YMnO3 epitaxial films at around the Néel temperature was investigated to discuss the effect of the antiferromagnetic ordering on the ferroelectric domain wall motion. From neutron diffractions to investigate the antiferromagnetic ordering and measurements of polarization-electric field, dielectric constant, and the time constant of the domain wall motion, the change of the domain wall motion is suggested at around 120 K, which is higher than the Néel temperature (~80 K).
Abstract: Thin films of mixtures of molybdenum silicate (MoSi2) and silicon (Si) (MoSiX, where the Mo to Si molar ratio = 1:X) were deposited on silicon nitride (Si3N4) polycrystalline substrates by radio-frequency magnetron sputtering using a target made of a mixture of MoSi2 and Si powders. The crystal structure of MoSiX thin films deposited on the Si3N4 substrate consisted of a mixture of a hexagonal phase and an unknown phase when X > 2.05. A thin film consisting almost entirely of the unknown phase could be deposited when X = 2.1−2.15. Molybdenum silicate can exist in the forms Mo3Si, Mo5Si3, or MoSi2, but to date there has been no report of molybdenum silicate having a Si to Mo molar composition ratio of larger than 2. It was found that the surfaces of thin films of the hexagonal phase or the unknown phase were readily oxidized, whereas the surfaces of thin films of a mixture of the hexagonal phase and the unknown phase exhibit excellent oxidation resistance in air at temperatures up to 700 °C.
Abstract: Resistance random access memory (RRAM) is attractive as a next-generation form of nonvolatile memory. We investigated an electric field-induced resistance change of SrFeO2+x film as a candidate for RRAM material. SrFeO2.5-x film prepared at 300 oC showed hysteresis in its current-voltage curve and distinct pulse-switching properties. On the other hand, the sample prepared below 280 oC showed hysteresis in its current-voltage curve but didn’t show pulse-switching properties. The amount of oxygen in the sample and easiness of oxygen migration play important roles in the resistance-switching properties.
Abstract: BaxSr1-xTiO3 (BST) thin films were deposited by modified CSD, in which partially hydrolyzed Ti-alkoxide was reacted with Ba-Sr precursor solution to form highly polymerized BST precursor solutions, leading to the better electrical properties of the resultant thin films. BST precursor solutions of 0.1 M were prepared to deposit BST thin layers of 17nm ~ 20nm for one dip-coating operation with different barium to strontium ratio of Ba/Sr = 90/10, 70/30 and 50/50. Modified CSD-derived BST thin films were deposited on a Si wafer with Pt electrode or CSD-derived LaNiO3 (LNO) seeding layer with preferred orientation. BST thin films exhibited ferroelectric or paraelectric properties, depending upon the Ba/Sr ratio. Better electrical properties for the BST thin films were observed on a LNO seeding layer. Maximum tunability of our BST film was 41 % at 1MHz.
Abstract: Thermal stability of bottom electrode thin films (La0.5Sr0.5)CoO3 (LSCO) and (La0.6Sr0.4)MnO3 (LSMO) were investigated. The crystallization and surface morphology of the heterostructure were characterized using x-ray diffraction and atomic force microscopy. Resistivity of the LSCO thin film was 25 cm. However, the resistivity of LSCO thin film increases sharply with annealing temperature. The LSMO thin film has high resistivity (100 mcm). The film does not decompose after thermal processing at 900 °C. To confirm thermal stability, we examined the effect of post annealing at various temperatures on the morphology and resistivity. Results showed that LSMO has higher thermal stability than that of LSCO.
Abstract: The HfO2 films were prepared on the ITO/polyimide substrate using alkoxy-derived precursor solutions at low temperature. The HfO2 films prepared by UV-assisted process using the precursor solution modified with diethanolamine had smooth surface and RMS roughness values of HfO2 film were 1.2nm. The electrical properties of HfO2 films were improved by optimization of preparation condition. The leakage current density at 1V was below 10-5A/cm2. The dielectric constant was about 20. The loss tangent was below 0.1.