Papers by Author: Nobuyasu Mizutani

Abstract: Pb(Zr, Ti)O3 thin films were successfully prepared on (111)Pt/IrO2/SiO2/(100)Si substrates using SrTiO3 seeds at 290 oC by RF inductive heating type and 350 oC by resistive heating type metalorganic chemical vapor deposition method (MOCVD), respectively. The SrTiO3 was chosen as seed layers and prepared by pulsed laser deposition method. The crystal structures and orientations of SrTiO3 seeds were changed by deposition temperature. In the case of preparation with RF inductive heating MOCVD, the remanent polarization (2Pr) and coercive field (2Ec) were 42 μC/cm2 and 256 kV/cm, respectively.

Abstract: Changes of residual stress and electrical properties were examined in (001)-oriented and (111)-oriented Pb(Zr0.5Ti0.5)O3 (PZT) thin films deposited on a buffered-Si substrate with a buffer and bottom electrode layer of a (La,Sr)CoO3(LSCO). A (001)-epitaxial PZT film was prepared on LSCO/CeO2 /Zr0.85Y0.15O1.93(YSZ)/Si. In addition, a (111)-oriented PZT film was prepared on LSCO/SrTiO3(ST) /Mn0.24Zn0.09Fe2.67O4(MZF)/YSZ/Si. The residual tensile stress in (001)-PZT thin films decreased from 2.92 to 1.98 GPa and the remanent polarization increased from 7.5 to 41.7 @C/cm2 as the LSCO thickness increased. In (111)-PZT, the residual tensile stress decreased from 1.72 to 0.95 GPa and remanent polarization increased from 9.5 to 26.7 @C/cm2. The residual tensile stress of (111)-PZT was less than that of (001)-PZT. The remanent polarization in the 80 nm (111)-PZT was greater than that of the 60 nm (001)-PZT. In the 700-nm-thick PZT, the remanent polarization in (001)-PZT was greater than that in (111)-PZT.

Abstract: Epitaxial LiTaO3 thin films were deposited on epitaxial Pt(111)/Al2O3(001) and Al2O3(001) substrates by metal organic chemical vapor deposition using LiTa(OC2H5)4(OC2H4OCH3)2 and Li(DPM) precursors. The full-width at half-maximum of the rocking curve of LiTaO3 thin films were respectively 0.29° on Al2O3(001) substrates and 0.98° on epitaxial Pt(111)/Al2O3(001). Electrical measurements showed that the remanent polarization and coercive field of the films were 2Pr=76 μC/cm2 and E
=130 kV/cm, respectively. The leakage current density was 10-6–10-8 A/cm2 at 120 kV/cm. Refractive indices n measured at 632.8 nm were measured respectively as 2.15 on Al2O3(001) and 2.14 on Pt(111)/Al2O3(001).

Abstract: Pb(Zr0.05Ti0.95)O3/(La,Sr)CoO3 thin films were prepared by pulsed laser deposition (PLD) on SrTiO3(001) substrates. Phase transition behavior of Pb(Zr0.05Ti0.95)O3 (PZT) was investigated using high temperature X-ray diffraction (HT-XRD) and high-temperature electrical measurement. The phase transition temperature of PZT thin film is larger than bulk one. In 100 and 200nm-thickness epitaxial PZT thin films, the phase transition temperatures obtained from X-ray diffraction measurement and electrical property measurement are in good agreement.

Abstract: In this study, BiFeO3 (BFO) epitaxial film was deposited on SrRuO3 (100)/SrTiO3 (100) substrates using pulsed laser deposition (PLD). Phase pure BFO thin film was obtained. Introducing a mask between the target and substrate in PLD improved the surface roughness from 47.8 nm (RMS, without mask) to 7.7 nm (RMS, with mask). The composition and electrical properties of BFO thin film were assessed after annealing for 1 h in Ar, N2, or O2 atmosphere at 600°C. The P-E hysteresis properties improved only in the O2 atmosphere. After annealing under O2 atmosphere, the leakage current decreased from 6.1 × 10-2 A/cm to 2.9 × 10-2 A/cm at 200 kV/cm, as in the other annealing atmospheres, but 2Pr increased from 35 BC/cm2 to 50 BC/cm2.

Abstract: Epitaxial Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) thin films for electrooptic applications were fabricated on a Si substrate using buffer layers. The PMN-PT/SrRuO3/SrTiO3/(La,Sr)CoO3/CeO2 /YSZ/Si hetrostructure was fabricated by pulsed laser deposition. A PMN-PT thin film with a thickness of 2μm was successfully deposited. The optical characteristics of PMN-PT epitaxial film were measured by prism coupling method. The morphology of the PMN-PT films was drastically improved by introducing a mask between the target and substrate during the deposition. The PMN-PT thin film showed a columnar structure, where the width of each column was approximately 180nm. A refractive index of 2.48 with zero bias voltage was obtained for the epitaxial PMN-PT thin film using the prism coupler method.

Abstract: Diffusion behavior at the interface of (001)-epitaxially grown (Ba,Sr)TiO3(BST)/electrode/buffer layer/Si thin films was examined by use of secondary ion-microprobe mass spectrometer (SIMS) and transmission electron microscope (TEM) attached with energy dispersive X-ray fluorescence spectrometer (EDX). As the (001)-epitaxially grown film, following three kinds of structure was grown; (1)BST/(La,Sr)CoO3(LSCO)/CeO2/yttria-stabilized zirconia(YSZ)/Si, (2)BST/PLD-deposited Pt/SrTiO3(ST)/LSCO/CeO2/YSZ/Si and (3)BST/sputter-deposited Pt/ST/LSCO/CeO2/YSZ/Si. For sample (1), uphill diffusion of Sr and Ti was observed at the interface of YSZ and SiO2. Diffusion of Co into CeO2 layer was also detected. These tendencies of diffusion were also observed for samples (2) and (3). In addition to these tendencies, apparent uphill diffusion of Co at the Pt layer was observed for sample (2). However, this diffusion was not observed for sample (3). It was also observed that oxygen diffusion was prevented for sputter-deposited Pt. On the other hand, oxygen diffusion was observed for PLD-deposited Pt.