Abstract
Interfacial structures of the Pt/SBT/Pt capacitors prepared by metallo-organic decomposition were examined by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) as a function of the postannealed time at 750°C to investigate the interfacial evolution developed in the Pt/SBT/Pt capacitors. The results show that after postannealing at 750°C for a short time (e.g., 300 s), a thin amorphous layer was observed at the interfaces of the SBT/Pt-bottom and the SBT/Pt-top electrodes in the Pt/SBT/Pt capacitors, whereas after postannealing for a moderate time (e.g., 20 min), the interfaces of the SBT/Pt-bottom and the SBT/Pt-top electrodes became quite smooth and uniform, and almost free of the interfacial phase. However, after postannealing for a longer time (e.g., 60 min), an interfacial phase consisting of oval-shaped nanocrystallites was developed at both the SBT/Pt-bottom and the SBT/Pt-top electrode interfaces, which resulted in weakly bonded interfaces between the SBT films and Pt electrodes. This is the reason why a Pt electrode peeling phenomenon (similar to that reported in the Pt/SBT/Pt/capacitors annealed in the forming gas atmosphere) is frequently observed in the Pt/SBT/Pt capacitors postannealed for 60 min during the fabrication of cross-sectional TEM samples. Based on two-dimensional lattice fringes of the HRTEM images from the small nanocrystallites and the corresponding fast Fourier transform patterns, the oval-shaped nanocrystallites precipitated at both the SBT/Pt-bottom and the SBT/Pt-top electrode interfaces were determined to be a PtBi2 phase with a cubic structure. The formation of the Pt–Bi-based interfaces in the Pt/SBT/Pt capacitors is due to the reaction of bismuth (out-diffused from the SBT films) with Pt electrodes during the postannealing process. The elliptical morphology of the interfacial PtBi2 phase can be ascribed to its different growth rates in the parallel and vertical directions of the interface, and also the limited space for grain growth perpendicular to the interface.
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