Preparation of ultra thin SrBi2Ta2O9 films using metalorganic chemical vapor deposition combined with a modified annealing method

We report a capacitor-preparation method using an ultra thin SrBi2Ta2O9 (SBT) film for application to low-voltage-operated ferroelectric random-access memories (FeRAMs). As the film thickness was reduced below 100 nm, the SET capacitor reached dielectric breakdown at a much lower electric field. Atomic force microscopy (AFM) analysis revealed that the crystallization annealing roughened the interface between the electrode and SET. We attributed the electrical breakdown to the localized electric field at the roughened interface. By modifying the annealing method for crystallization of SET, the interface was maintained smooth and flat even after the crystallization annealing, resulting in good performance in terms of the leakage current vs. appled voltage (I-V) characteristics. Employing a 50 nm thick SET film, by the modified annealing method, a low-voltage operation as well as highly insulating properties was realized: the remanent polarization (2P(r)). coercive field (V-c) and leakage current density (J) at 1.5 V were 12.2 muC/cm(2), 0.36 V and approximately 5 x 10(-9) A/cm(2), respectively.