A Superlattice Approach to the Synthesis of Strontium Bismuth Tantalate thin films using Liquid-Injection-MOCVD
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0902-T02-02.1
A SUPERLATTICE APPROACH TO THE SYNTHESIS OF STRONTIUM BISMUTH TANTALATE THIN FILMS USING LIQUID-INJECTION-MOCVD RICHARD J. POTTER,a AHMED AWAD,a PAUL R. CHALKER,a PENG WANG,a ANTHONY C. JONES,b,c TIMOTHY C.Q. NOAKES d AND PAUL BAILEY.d a
Department of Engineering, University of Liverpool, Liverpool, L69 3BX, UK Department of Chemistry, University of Liverpool, Liverpool, L69 7ZD, UK c Epichem Ltd., Power Road, Bromborough, Wirral, Merseyside, CH62 3QF, UK d CCLRC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD, UK b
ABSTRACT The synthesis of SrBi2Ta2O9 (SBT) thin films has been investigated using a superlattice approach. Thin films were deposited on silicon by independent injection of each source to produce Bi2O3/SrTa2O6 superlattices. The effects of post-deposition annealing have been investigated using high-resolution TEM and medium energy ion scattering (MEIS) to depth profile the superlattices. X-ray diffraction has also been used to characterize the conversion of the superlattices from distinct layers of Bi2O3 and SrTa2O6 into a polycrystalline layer of strontium bismuth tantalate. 1. INTRODUCTION Non-volatile ferroelectric random access memories (NV-FeRAM) is widely considered as the ideal non-volatile memory with highly desirable performance features, such as high write speeds, low power operation, high endurance (read-write cycles) and high radiation hardness. Strontium– bismuth–tantalate, SrBi2Ta2O9 (SBT), and related materials such as SrBi2(TaxNb1-x)2O9 (SBTN), are promising materials for use in NV-FeRAM applications as they have been shown to have excellent resistance to fatigue degradation.[1,2] The ferroelectric phase of SBT(N) is a layered bismuth oxide belonging to the m=2 Aurivillius family, which can be viewed as alternating Bi2O3 sheets and SrTa2O6 double perovskite-like layers. SBT films have been deposited by a variety of techniques including metalorganic decomposition,[3] pulsed laser ablation [4] and metalorganic chemical vapour deposition (MOCVD).[5-8] In MOCVD the metal is transported in the vapour phase as a volatile metalorganic compound, which thermally decomposes, usually in the presence of oxygen, on a heated substrate (e.g. Si, SiO2, SrTiO3). MOCVD has a number of advantages over the other deposition techniques as it offers the potential for large area growth, excellent film uniformity, composition control, high film densities, high deposition rates and excellent conformal step coverage at device dimensions of less than 2 µm.[9] Furthermore, the MOCVD technique is compatible with existing processes used in silicon VLSI and ULSI device fabrication. The development of MOCVD for the deposition of SBT has been restricted by a lack of suitable precursors. Conventional precursors, such as Sr(thd)2 (thd = 2,2,6,6-tetramethylheptane-3,5dionate), Bi(C6H5)3, BiMe3, Bi(OtC5H11)3, Ta(OEt)5 and Ta(OPri)4(thd),[10,11] have very different physical properties and decomposition characteristics. This mismatch can results in poor film uniformity, composition control problems and reduc
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