Leakage Current of PLD- and CSD-BiFeO 3 Thin Films Observed by Current Sensitive AFM
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1199-F06-21
Leakage Current of PLD- and CSD-BiFeO3 Thin Films Observed by Current Sensitive AFM Seiji Nakashima1, Hironori Fujisawa1, Jung Min Park2, Takeshi Kanashima2, Masanori Okuyama2, and Masaru Shimizu1 1 Depattment of Electrical Engineering and Computer Sciences, Graduate School of Engineering, University of Hyogo, 2167, Shosya, Himeji, Hyogo, 671-2280, Japan. 2 Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, 1-3, Machikaneyama-cho, Toyonaka, Osaka, 560-8531, Japan. ABSTRACT We have investigated relationships between leakage current and microstructure or domain structure of BiFeO3 (BFO) thin films, and leakage current mappings of BFO thin films have been performed by current sensitive AFM. 350-nm-thick and 250-nm-thick BFO thin films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) and chemical solution deposition (CSD), respectively. Average grain size of PLD-BFO thin film is about 480 nm, which is the same as the film thickness. From the leakage current mapping at a bias voltage of -16 Vdc, leakage current of the BFO thin film flows through not only grain boundary but also the grain itself. On the other hand, CSD-BFO thin film shows rosette structure and small size grains. From the leakage current mapping at a bias voltage of -10 Vdc, leakage current flows along boundaries of the rosette structures. These results indicate that leakage current of BFO strongly depends on its microstructure. . INTRODUCTION Multiferroics have attracted much attention because of simultaneous existence of (anti)ferroelectricity, (anti)ferromagnetism and ferroelasticity from a viewpoint of practical applications such as memories, sensors and actuators. These properties are due to their strong coupling between electric polarization and elastic strain [1-3]. Moreover, most of multiferroic materials are Pb-free and expected as alternative lead-free ferroelectrics or piezoelectrics from the view point of environmental ecology although PbZr1-xTixO3 (PZT) is used as the most popular ferroelectric and piezoelectric materials. Among many multiferroic materials, BiFeO3 (BFO) with ABO3 type perovskite structure is the leading candidate, which shows good ferroelectric properties in thin film form [4]. Crystal structure of bulk BFO is rhombohedrallydistorted perovskite structure belonging to space group of R3c with lattice parameter of ahex = bhex = 0.571(5) nm and chex = 1.3858(5) nm [5]. The noncentrosymmetric-distorted structure which takes an important role for ferroelectricity is stabilized by Bi – O bond with strong covalent characteristics of the 6s2 lone pair in Bi3+. In a recent report, BFO single crystal shows remanent polarization (Pr) of 60 μC/cm2 along [012]hex direction [5, 6]. On the other hand, we have reported that polycrystalline BFO thin film deposited on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) shows giant ferroelectric polarization (Pr ~ 152 μC/cm2) at 80 K
TABLE I PLD conditions for BFO deposition Target Substrate Sub. Temp. Gas P
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