THICKNESS DEPENDENCE OF THE COERCIVE FIELD IN FERROELECTRIC THIN FILMS

By considering the effects of the space charges and domain boundaries in ferroelectric thin films, the thickness dependence of coercive field (Ec) is numerically simulated based on the four-state Potts model with the nearest-neighbor interactions between dipole moments. For large thickness, experimental results where Ec decreases with thickness can be produced from our Monte-Carlo simulation. On the other hand, when the thickness is very small, our simulation gets that Ec increases with thickness by the study of the polarization switching in the film. This gives an explanation of the experimental result by Zhu et al. in J. Appl. Phys.83, 1 (1998) for SBT-BTN film, and a similar report by Bune et al. in Nature391, 874 (1998) for the crystalline film. The critical temperature of the thin film is also discussed.