Stress Dependence of Crystal Structure of Polycrystalline BiFeO 3 Thin Films on Membrane Structure Prepared by Pulsed La
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1034-K03-09
Stress Dependence of Crystal Structure of Polycrystalline BiFeO3 Thin Films on Membrane Structure Prepared by Pulsed Laser Deposition Seiji Nakashima1, Dan Ricinschi1, Yoshitaka Nakamura1, Masanori Okuyama1, Hironori Fujisawa2, and Masaru Shimizu2 1 Division of Advanced Electronics and Optical Science, Department of Systems Innovation, Graduate school of Engineering Science, Osaka University, 1-3 Machikaneyakma-cho, Toyonaka, 560-8531, Japan 2 Department of Electrical Engineering and Computer Sciences, Graduate school of Engineering, University of Hyogo, 2167 Syosya, Himeji, 671-2201, Japan
ABSTRACT An Influence of stress of crystal structure of polycrystalline BiFeO3 (BFO) thin film on membrane structure has been investigated. To confirm the stress dependence of the crystal structure, reciprocal space mapping measurement of polycrystalline BFO thin films on Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (625 µm) plate substrate and Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (15 µm) membrane substrate have been performed. These BFO thin films have been prepared by pulsed laser deposition (PLD). The obtained BFO thin films were polycrystalline and mainly oriented to (001) and (110) plane. From reciprocal space mapping measurement, (110) oriented BFO grains on Pt/TiO2/SiO2/Si (15 µm) membrane substrate were expanded perpendicularly to the film plane about 0.15% and compressed in parallel to the film plane about 0.7% comparing to that on Pt/TiO2/SiO2/Si (625 µm) plate substrate. And (001) oriented BFO grains on the Pt/TiO2/SiO2/Si membrane substrate were expanded about 0.20% perpendicularly to the film plane and compressed about 1.3% in parallel to the film plane comparing to that on Pt/TiO2/SiO2/Si (625 µm) plate substrate.
INTRODUCTION Multiferroic materials such as BiFeO3 (BFO), YMnO3, TbMnO3 have much attracted considerable interest due to simultaneous existence of ferroelectricity, ferromagnetism (or antiferromagnetism) and ferroelastisity. Especially, TbMnO3 shows new types of ferroelectricity, and large magnetoelectric (ME) effect [1]. Among these multiferroic materials, BFO is expected to show strong coupling of ferroelectric and antiferromagnetic ordering at RT because of its high Curie temperature (TC ~ 850 oC) and Neel temperature (TN ~ 370 oC) [2, 3]. Moreover, BFO is also expected as lead-free ferroelectrics due to showing large ferroelectric polarization in thin film form [4-7]. Crystal structure of bulk BFO is rhombohedrally distorted perovskite structure belonging to space group of R3c with lattice parameter of a = 0.562 nm and α = 59.35o [8]. On the other hand, epitaxial BFO thin films on SrTiO3 (001) single crystal substrate show 50 to 60 µC/cm2 [5, 6]. Epitaxial BFO thin films have monoclinic structure due to epitaxial strain from cubic SrTiO3 single crystal. Furthermore, polycrystalline BFO thin films on
Pt (200 nm) BFO (350 nm) Pt (200 nm) TiO2 (50 nm) SiO2 (600 nm)
Si (625 µm)
(a)
Si (15 µm)
(b)
Figure1. Schematic diagrams of fabricated sample of BFO thin film on (a) Pt/TiO2/SiO2/S
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