Transmission electron microscopy investigation of Pt/Ba_0.7Sr_0.3TiO₃/Pt capacitors with different annealing processes

The effects of postannealing in oxygen ambient and forming gas atmosphere (FGA) on the microstructure and chemistry of Pt/Ba_0.7Sr_0.3TiO₃ (BST)/Pt capacitors prepared by chemical solution deposition have been investigated by means of transmission electron microscopy. The as-deposited film layers of the Pt/BST/Pt capacitors show a columnar structure. The postannealing in O₂ leads to a smoothness of the top film-electrode interface. The additional FGA treatment applied to the postannealing capacitors introduces disordered or amorphous regions at both top and bottom interfaces. In these regions, deviation in composition from the stoichiometry occurs with a higher Ti/(Ba + Sr) ratio. These amorphous regions are believed to be responsible for the increase of the leakage current obtained in the FGA-treated capacitors. The thickness of this amorphous interfacial layer can be reduced significantly by a recovery annealing process in air at low temperatures.