Preparations and Characterizations of Epitaxial SrBi 2 Ta 2 O 9 Thin Films

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Preparations and Characterizations of Epitaxial SrBi2Ta2O9 Thin Films Keisuke Saito1, Masatoshi Mitsuya2, Toshimasa Suzuki3, Yuji Nishi3, Masayuki Fujimoto3, Masanori Nukaga2, Isao Yamaji1, Takao Akai1 and Hiroshi Funakubo2 1

Application Laboratory, Philips Japan Ltd.

7-35-1 Sagamiono, Sagamihara 228-0803, Japan 2

Department of Innovative and Engineered Materials, Interdisciplinary Graduate School, Tokyo

Institute of Technology 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan 3

Taiyo Yuden Co., Ltd., 5607-2 Nakamuroda, Haruna-machi, Gumma 370-3347, Japan

ABSTRACT Epitaxial (001)-, (116)- and pseudo (103)-oriented Sr0.35Bi2.2Ta2O9 (SBT (0.35/2.2/2.0)) films were successfully grown on (001), (110) and (111) SrTiO3 substrates, respectively. High-resolution X-ray diffraction reciprocal space mapping (HRXRD-RSM) measurements and pole figure measurements clearly indicated that the (116)-oriented SBT

(0.35/2.2/2.0)

film consisted of two

growth domains those c-axis are separated 180° apart in in-plane and pseudo (103)-oriented SBT film consisted of three growth domains those c-axis are separated 120° apart in in-plane. Moreover, lattice parameter measurements indicated that SBT films grew in fully relaxed state. INTRODUCTION Bismuth layer structured ferroelectric materials, such as SrBi2Ta2O9 (SBT) and Bi4Ti3O12 (BIT), have attractive attention for ferroelectric random access memory (FeRAM) application.1 SBT, in particular, has been widely studied and recently, the FeRAM consisted of SBT capacitor has been commercially available. However, the character of SBT crystal in the form of thin film has not been fully understood yet. Therefore, it is important to investigate the physical properties including growth mechanism on crystalline substrate using epitaxial grade SBT film is highly desired. From Rietveld refinement using X-ray and neutron for SBT polycrystalline powder material, the lattice parameters and crystal symmetry of SBT crystal was identified.2-4 The refined space group, A21am, indicates that the mirror plane exists parallel to a-b plane, therefore, the spontaneous polarization is expected not to exist along c-axis of SBT unit cell. This leads extensive interest on controlling the preferred orientation of SBT crystal. From the practical point of view, SBT film is prepared on fiber textured conductive bottom electrodes, such as Pt1, CC10.13.1

and IrOx5, and typically these bottom electrodes materials have (111) preferred orientation when those are grown on conventional oxidized (001) Si substrate. Recently, we reported that the SBT film grown on (111) preferentially oriented Pt bottom electrode grown by MOCVD has {103} preferred orientation.6 We attributed the preferentially oriented SBT film growth to the local epitaxial growth between (111) oriented Pt bottom electrode and {103} SBT. In fact, the lattice mismatches between (111) Pt and (103) SBT are estimated to be 0.14% along [010] SBT and 4.5% along [10 3 ] SBT and these rather small lattice mismatches are probably sufficient for promoting epit

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