Ferroelectric random access memory with high electric properties and high production yield realized by employing an AlO_x underlying layer of Pt bottom electrode for a La-doped lead zirconate titanate capacitor

Abstract

Although ferroelectric random access memory (FRAM) has superior electric properties, its downside is that it has a relatively larger cell area in comparison other non-volatile memories. We tried to apply TiO x , and AlO x to an underlying layer (TiO x -UL, AlO x -UL) instead of our previously used Ti underlying layer (Ti-UL) for the La-doped lead zirconate titanate (PLZT) capacitor to obtain a high polarization value aiming to a lowering cell area. The failed bit ratio of the FRAM with TiO x -UL was found to be higher than that with AlO x -UL even though polarization values of the PLZT capacitor with both underlying layers are almost the same and much higher than that with Ti-UL. It is strongly suggested that the imprint induced in PLZT by charged defect is a main cause of bit failure by fail-bit analysis. X-ray diffraction and atomic force microscopy observations shows that charged defect density in PLZT over TiO x -UL is possibly higher than that in PLZT over AlO x -UL due to surface roughness of underlying layers.