Electrical Properties of Bi 3.25 La 0.75 Ti 3 O 12 Thin Films with Various Grain Orientations Deposited by r.f. Magnetro
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G3.15.1
Electrical properties of Bi 3.25 La 0.75 Ti3O12 thin films with various grain orientations deposited by r.f. magnetron sputtering Ju Hyung Suh1, Sang Ho Oh1,2 and Chan-Gyung Park1 1 Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea 2 Max-Planck-Istitut für Metallforschung, Heigenbergstrasse 3, 70569 Stuttgart, Germany ABSTRACT Effects of grain orientation on the electrical polarization and leakage current characteristics of Bi3.25La0.75Ti3O12 (BLT) thin films have been investigated with respect to c-axis off-alignment. The BLT thin films from epitaxially aligned along c-axis to (117) and (014) off-aligned orientations have been successfully grown by using both different electrode materials (Pt and SrRuO3) and heat-treatments. In order to evaluate the crystallinity and the film texture of various off-aligned BLT thin films, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were carried out. The BLT thin films deposited on SrRuO3/SrTiO3 (100) substrate was grown epitaxial c-axis alignment. That is, the c-axis of the film was completely parallel to the substrate normal, resulting in a cube on cube epitaxial relationship with the underlying SrRuO3 film. The corresponding P-E curve showed nearly paraelectric property. The polycrystalline (117) and (014) oriented BLT thin films revealed that remnant polarization increased remarkably due to the anisotropy of spontaneous polarization of BLT. The surface roughness of BLT thin films was increased to result in degraded leakage current characteristic. According to the present results, it can be concluded that the grain orientation of BLT thin films is a crucial factor controlling the polarization properties and leakage current characteristics. INTRODUCTION Non-volatile ferroelectric random access memory (NVFRAM) is an alternative memory because of its potential advantages, such as high density of dynamic random access memory, fast access time of synchronous DRAM and non-volatile property of flash memory. As a candidate for the capacitor of high density NVFRAM, many ferroelectric materials have been developed. In fact, PbZr1-xTixO3 (PZT) and SrBi2Ta2O9 (SBT) have been used for commercial products. However, PZT films deposited on metal electrodes showed prominent degradation of polarization after many read/write cycles (so called fatigue) and SBT films showing a low remnant polarization required high deposition temperature. As an other candidate material,
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Bi3.25La0.75Ti3O12 (BLT) films1, in which bismuth is substituted by lanthanum to improve the fatigue property of Bi4Ti3O12 (BTO), has been considered, because it showed fatigue-free property on metal electrodes with a large remnant polarization (2Pr, 16~20 µC/cm2) and lower de
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