An optimized process for fabrication of SrBi 2 Ta 2 O 9 thin films using a novel chemical solution deposition technique
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An optimized process for fabrication of SrBi2Ta2O9 thin films using a novel chemical solution deposition technique Seung-Hyun Kim, D.J. Kim, K.M. Lee, M. Park, and A.I. Kingon Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695
R.J. Nemanich Department of Physics, North Carolina State University, Raleigh, North Carolina 27695
J. Im and S.K. Streiffer Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (Received 30 October 1998; accepted 18 August 1999)
Ferroelectric SrBi2Ta2O9 (SBT) thin films on Pt/ZrO2/SiO2/Si were successfully prepared by using an alkanolamine-modified chemical solution deposition method. It was observed that alkanolamine provided stability to the SBT solution by retarding the hydrolysis and condensation rates. The crystallinity and the microstructure of the SBT thin films improved with increasing annealing temperature and were strongly correlated with the ferroelectric properties of the SBT thin films. The films annealed at 800 °C exhibited low leakage current density, low voltage saturation, high remanent polarization, and good fatigue characteristics at least up to 1010 switching cycles, indicating favorable behavior for memory applications.
I. INTRODUCTION
II. EXPERIMENTAL
In recent years, ferroelectric thin films have been extensively investigated for nonvolatile memory applications.1–3 Although Pb(ZrxTi1−x)O3 (PZT) materials have been considered to be promising candidates for these applications,4–6 PZT thin films undergo severe polarization fatigue with metal electrodes,6,7 which may limit their applicability. Recently, it has been reported that Sr Bi2Ta2O9 (SBT) layer-structured ferroelectric thin films have high potentials for memory applications due to good fatigue resistance and low voltage polarization switching.8,9 Among various preparation techniques for SBT thin films, chemical solution deposition (CSD) is promising because it provides high purity, large deposition area, and easy composition control.10,11 However, a stable, simple preparation process for SBT solutions has not previously been reported due to limitations of preferred precursors. In this study, a new chemical route using an alkanolamine as a chelating agent is suggested. It is found that a particular chelating agent increases the stability of the SBT solution. The optimal processing window for producing SBT thin films using this new chemical solution method is reported here. We also make a comparative investigation of surface microstructures, crystallization behaviors, and related ferroelectric properties for SBT thin films prepared using this method as a function of annealing temperature.
The choice of precursors, solvents and chelating agents is very important for producing high-quality thin films using chemical solution deposition (CSD) processing. In this work, SBT solution (Sr/Bi/Ta ⳱ 0.8/2.3/2) was prepared using Sr–acetate [Sr(CH3CO2)2], Bi–nitrate [Bi(NO3)3 䡠 5H2O], and T
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