Pt nanocrystalline interfacial layer in an SBT/Pt/Ti ferroelectric capacitor

The microstructural feature of platinum (Pt) bottom electrode in a strontium-bismuth-tantalate (SBT)/Pt/titanium (Ti) stack was investigated by field-emission transmission electron microscopy. The appearance of a thin nanocrystalline Pt (nano-Pt) interfacial layer was unexpectedly observed in the SBT/Pt interface region after crystallization treatment. The energy-dispersive spectrometer analyses indicated a great amount of TiO_x formed along the grain boundaries of this nanocrystalline layer. Such a phenomenon is strongly related to the grain-boundary diffusions of O and Ti atoms during the annealing process in oxygen ambient. It is speculated that the structural reconstruction of the Pt electrode was likely triggered by the compressive stress due to the large volume expansion during TiO_x growth. Under such compressive stress and thermal conditions, Pt may be plastically deformed and inclined to recover and recrystallize into the nanocrystalline structure. Because the emergence of TiO_x, in nano-Pt/columnar-Pt interfacial regions would significantly deteriorate the continuity and the ductility of Pt electrode, it possibly causes the peeling of SBT layer and poses a serious problem to the integration of the ferroelectric capacitors.