Combined piezo-force microscopy and conductive atomic-force microscopy for investigating leakage current conduction and local domain structure of PbTiO3 thin films

Local ferroelectric properties and leakage current behaviors of atomic-layer-deposited PbTiO3 (PTO) thin films on Ir electrode were investigated by piezo-force microscopy (PFM) and conductive atomic-force microscopy (CAFM). The as-grown PTO thin films were amorphous due to their low growth temperature (200 degrees C). Post-deposition annealing (PDA) at 600 degrees C for 30 min under O-2 atmosphere using furnace crystallized the stoichiometric (Pb/Ti atomic ratio similar to 0.97) films into perovskite structure. The film morphology was critically dependent on the heating schedule during PDA; fast heating and cooling (< 5 min) resulted in a crystallized film with the rough and irregular morphology whereas the slow heating and cooling (> 60 min) resulted in a film with better morphology. The leakage current of the former case was much higher than that of the latter. The large leakage current adversely interferes with the polarization of the film during the PFM measurement. However, the local leakage current did not show any clear correlation with the local ferroelectric status of the grains and morpological changes.