Combined piezo-force microscopy and conductive atomicforce 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 atomicforce microscopy (CAFM). The as-grown PTO thin films were amorphous due to their low growth temperature (200°C). Post-deposition annealing (PDA) at 600°C for 30 min under O₂ atmosphere using furnace crystallized the stoichiometric (Pb/Ti atomic ratio ∼ 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.