Papers by Author: Hiroshi Uchida

Abstract: One-axis-oriented Pb (Zr,Ti)O₃ (PZT) films were fabricated using a chemical solution deposition technique on (111)Pt/TiO₂/(100)Si and Inconel625 substrates buffered by nanosheet Ca₂Nb₃O₁₀ (ns-CN). The (001)-oriented PZT crystals (Zr/Ti=0.40:0.60, tetragonal) were preferentially grown on (001)ns-CN/Inconel625, whereas the PZT crystals deposited on (001)ns-CN/(111)Pt/ TiO₂/(100)Si exhibited preferential PZT(100) orientation. The resulting PZT film on (001)ns-CN/Inconel625 indicated remanent polarization of approximately 59 μC/cm², which was significantly larger than that on (001)ns-CN/(111)Pt/TiO₂/(100)Si.

Abstract: Thin films of (La,Sr)MnO₃ (LSMO) were fabricated by industrial-versatile chemical solution deposition (CSD) technique. Well [100]-oriented LSMO films were fabricated at 650-750 °C by use of buffer layers of LaNiO₃ buffer layer on a silicon substrate. The product of lower electrical resistivity is promising as an electrode of fatigue-free ferroelectric capacitor.

Abstract: Bi-based perovskite-type oxide materials such as BiFeO₃ (BFO) and Bi (Zn_1/2Ti_1/2)O₃ and the related compounds receive much attention and have been developed actively as important candidates for Pb-free ferroelectric materials instead of toxic Pb-based perovskite oxide materials. Recently, many researches have been reported for thin films of Bi-based materials by various film-deposition techniques for actual application of semiconductive devices, microactuators, etc. In this study, we tried preferential crystal growth of BFZT films on semiconductive silicon substrates using uniaxial-(100)-oriented LaNiO₃ (LNO) buffer layer. BFO films were fabricated via chemical solution deposition (CSD) technique on platinized silicon wafer [(111)Pt/TiO₂/(100)S and (100)LNO-coated platinized silicon [(100)LNO/(111)Pt/TiO₂/(100)S substrates. XRD analysis indicated that the films fabricated on (111)Pt/TiO₂/(100)Si substrate consisted of randomly-oriented BFZT crystal with lower crystallinity. On the other hand, the films on (100)LNO/(111)Pt/TiO₂/(100)Si consisted of uniaxial-one-oriented BFZT crystal with higher crystallinity. The crystallization temperature these films were 500°C, respectively. These results suggest that the BFZT crystal was grown successfully on uniaxial oriented (100)LNO plane which also had perovskite-type crystal structure. Consequently, one-oriented BFZT films were prepared on Si substrate successfully using (100)LNO buffer layer.

Abstract: Thin films of MBi₄Ti₄O₁₅ (M = Ca and Sr) with preferential crystal orientation were fabricated using underneath perovskite layers on various substrates. One-axis BLSD films on (100)LaNiO₃/(111)Pt/Ti/(100)Si and epitaxial BLSD films on (100)SrRuO₃//(100)SrTiO₃ were fabricated by chemical solution deposition (CSD). Dielectric constants of the CaBi₄Ti₄O₁₅ and SrBi₄Ti₄O₁₅ films on (100)LaNiO₃/(111)Pt/Ti/(100)Si were approximately 250, while those on (100)SrRuO₃//(100)SrTiO₃ were 220, respectively. The temperature coefficients of capacitance (TCCs) of these films were below 10% in atmospheric temperature range between R.T. and 300°C, which is significantly smaller than those of conventional (Ba,Sr)TiO₃-based capacitors.

Abstract: Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement and a transmittance electron microscope (TEM) observation confirmed the formation of perovskite BT and ST nanocube particles with sizes of around 17 nm. These nanocube particles were monodistributed in hexane with tri-n-butylphosphine oxide (TBPO) as dispersant, separately, and then, the accumulations composed of the BT and ST nanocubes were built up using a selective catalytic reaction between 3-bromopropylphosphonic acid (BP) and aminomethylphosphonic acid (AM) as smart glue. The TEM observation confirmed that a part of accumulations showed a hetrointerface connection between BT and ST.

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: Barium titanate (BaTiO3, BT) and strontium titanate (SrTiO3, ST) nanocube particles were successfully prepared by a solvothermal method. The prepared particles were collected by a centrifugal separator. The X-ray diffraction (XRD) measurement confirmed the formation of perovskite BT and ST nanoparticles with sizes of around 17 nm while a transmittance electron microscope (TEM) observation revealed formation of cubic-shaped nanoparticles with sharp edge and corner. These nanocube particles were monodistributed in hexane with tri-n-octylphosphine oxide (TOPO) as dispersant, separately, and then, the 2-dimentional checkerboard-structured accumulations composed of the BT and ST nanocubes were built up using DNA base pair such as adenine and thymine as smart glue. TEM observation confirmed that a part of accumulations had a checkerboard-structure.

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: Thin films of titanium oxide (TiO2) were synthesized from Titanium diisopropoxide bis(dipivaloylmethanate) [Ti(O-i-Pr)2(dpm)2] as a source material using supercritical carbon dioxide (CO2) fluid. Flat films with a uniform microstructure were fabricated on SiO2/(100)Si substrates at a fluid pressure of 8.0 MPa, while granular particles were deposited on the film surface at a fluid pressure of 10.0 MPa. TiO2 films fabricated in supercritical CO2 atmosphere at 10.0 MPa were crystalline at the reaction temperature of 100°C, which was significantly lower than those in the conventional film-deposition techniques.

Abstract: The electrical properties of perovskite-based ferroelectric films were improved by ion modification using rare-earth cations. Thin films of rare-earth-modified lead zirconate titanate [Pb(Zr,Ti)O3] were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition technique. The substitution of volatile cations in the simple-perovskite oxides, such as Pb2+ in Pb(Zr,Ti)O3 films, enhanced the insulating properties of the film. The crystal anisotropy of the Pb(Zr,Ti)O3 film could be controlled by varying the species and the amount of replacing cations to enhance the spontaneous polarization. Thus, ion modification using Dy3+ cation could enhance the remanent polarization of Pb(Zr,Ti)O3 film consequently.