Papers by Author: Hiroshi Funakubo

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: 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: Micro-patterned Pb(Zr,Ti)O3 (PZT) films with dot-pattern were grown by metal organic chemical vapor phase deposition (MOCVD). Micro-patterned Pb(Zr,Ti)O3 (PZT) films were formed on dot-patterned SrRuO3 (SRO) buffer layer that was prepared by MOCVD through the metal mask on (111)Pt/Ti/SiO2/Si substrate. The orientation of dot-patterned PZT films was ascertained by the micro-beam x-ray diffraction (XRD) and their crystallinity was characterized by Raman spectroscopy. It was found that PZT films were oriented to (111) on dot-pattern, while (100)/(001) out of dot-pattern and the amount of oxygen vacancies at the circumference of the dot-pattern were larger than that of center of dot-pattern.

Abstract: (100)/(001)-oriented PZT thick films were grown on SrRuO3//(100) SrTiO3 and (100) MgO substrates by matel organic chemical vapor deposition (MOCVD) with different volume fraction of (001) orientation, and were compared with (001) single-oriented epitaxial PZT thick films grown on SrRuO3//LaNiO3//(100) CaF2 by polarized Raman spectroscopy. The spectra from (100)-oriented domain and (001)-oriented domain can be individually observed for the films with the mixture orientation of (100)/(001). Raman analysis revealed the different strain state of (100)-oriented and (001)-oriented domains. Moreover, the rotation dependence of A1(1TO) mode could be explained by the calculation using the volume fraction of (001)-oriented domains obtained from X-ray reciprocal space mapping analysis for the films with the mixture orientation of (100)/(001). These results suggest the local structure characterized by Raman spectroscopy almost agreed with the structure characterized by XRD analysis for the films with the mixture orientation of (100)/(001).

Abstract: The deposition mechanism of metal-Ru films including incubation time was investigated for Ru films prepared by metal organic chemical vapor deposition from (2,4-Dimethylpentadienyl)(ethylcyclopentadienyl)Ruthenium (DER) - O2 system. Substrates with amorphous top-layer having various Hf/Si ratio, SiO2 (native oxide)/(001)Si (SiO2), HfSiON/SiON/(001)Si (HfSiON) and HfO2/SiON/(001)Si (HfO2), were used as substrates. The deposition temperature dependence of the deposition amount at the fixed deposition time ranging from 210 oC to 300 oC revealed that the deposition amount depended on the deposition temperature below 250 oC, while it was almost constant above this temperature. Incubation time depended on the kinds of substrate at 210 oC and the substrate surface was fully covered in a shorter time with smaller deposition amount for the substrates with shorter incubation time. In addition, the film with shorter incubation time had smaller surface roughness.

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: Bismuth cuprate superconductor has a unique structure called a structural modulation (supercell, SC) consisting of modulated several unit cells. Strain induced by multilayered structure increases the intensity of SC modulation, while an oxygen deficient sample shows expansion of SC size. In this study, as opposed to the multilayer strain, by preparing samples with thick film thicknesses the effect of strain on crystal structure was investigated including SC structure. Epitaxial growth was verified by x-ray diffraction, and the thicker film showed other epitaxial phase rotated 32° around the surface normal with respect to the initial epitaxial phase. The SC size estimated by x-ray reciprocal space mapping was double the size of the initial epitaxial phase. Interestingly, the initial epitaxial phase became a dominant structure after further deposition. In order to evaluate the different SC size and SC modulation, a new index related with an incline of the modulation vector was proposed.

Abstract: (001)-, (1110), and (105)- oriented SrBi4Ti4O15 films with its c-axis tilted 0, 45 and 55o from the surface normal were epitaxially grown by metal organic chemical vapor deposition and the temperature dependency of the dielectric constant was systematically investigated. Relative dielectric constant, εr, and its temperature dependency increased when the tilting angle of the c-axis from the substrate surface normal increased. Temperature dependency of εr was positive in case of the (105) and (1110) orientation, which is in good agreement with the conventional ferroelectric materials. On the other hand, it became negative for (001) orientation. This shows the orientation dependency of εr in SrBi4Ti4O15.

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.