Direct Comparison of Structural and Electrical Properties of Epitaxial (001)-, (116)-, and (103)-Oriented SrBi 2 Ta 2 O
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Direct Comparison of Structural and Electrical Properties of Epitaxial (001)-, (116)-, and (103)-Oriented SrBi2Ta2O9 Thin Films on SrTiO3 and Silicon Substrates H. N. Lee, A. Pignolet, S. Senz, C. Harnagea, and D. Hesse Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle/Saale, Germany
ABSTRACT
Anisotropies of the properties of the bismuth-layered perovskite SrBi2Ta2O9 (SBT) have been investigated using epitaxial thin films grown by pulsed laser deposition both on conducting Nb-doped SrTiO3 (STO) single crystal substrates and on Si(100) substrates. It has been found that the three-dimensional epitaxy relationship SBT(001)||STO(001); SBT [1 1 0] ||STO[100] can be applied to all SBT thin films on STO substrates of (001), (011), and (111) orientations. An about 1.7 times larger remanent polarization was obtained in (103)-oriented SBT films than in that of (116) orientation, while the (001)-oriented SBT films revealed no ferroelectricity along their c-axis. Non-c-axis-oriented SBT films with a well-defined (116) orientation were also grown on silicon substrates for the first time. They were deposited on Si(100) covered with a conducting SrRuO3 (110) bottom electrode on a YSZ(100) buffer layer.
INTRODUCTION
Getting epitaxial SrBi2Ta2O9 (SBT) films (a = 0.5531 nm, b = 0.5534 nm, and c = 2.4984 nm [1]) is an important issue for applications in high-density ferroelectric random access memories (FRAMs). Epitaxial films are needed to overcome the problems related to the lack of uniformity in polycrystalline films [2]. The latter arise, because in high-density memories the lateral sizes of the individual structures approach both the sizes of the grains in polycrystalline films and the size of the ferroelectric domains. One solution to circumvent these non-uniformity problems is to use epitaxial thin films. As the vector of the spontaneous polarization (Ps) in SBT is directed perpendicularly to the c axis, specifically along its a axis, the growth of non-c-axisoriented SBT films is of particular significance for applications to planar-capacitor-type FRAMs. The epitaxial growth of SBT films both with c-axis and non-c-axis orientations was investigated on single crystal substrates such as SrTiO3 (STO), LaSrAlO4, etc. [3-5]. Particularly, the epitaxial orientation relationship of either SBT or SrBi2Nb2O9 (SBN) films grown on (011)- and (111)oriented STO substrates has been debated, for instance whether the (001) plane of SBT or SBN films is exactly parallel to the (001) plane of STO substrates in the non-c-axis-oriented SBT/SBN films with (116) and (103) orientations on STO(011) and STO(111) substrates [3-5], or whether a small deviation occurs. In this work, we report the epitaxial orientation relationship investigated by means of x-ray diffraction φ scans as well as a comparison between the structural and electrical properties of c-axis and non-c-axis-oriented SBT films grown on STO and on Si(100) substrates. For the application of epitaxial films in high-density ferroelectric nonvolatile memories, non-c-a
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