Depolarization fields in thin ferroelectric films

A mechanism is proposed to explain depolarization phenomena that have been observed in thin ferroelectric films and related multilayer devices. It is shown that, for a short-circuited electrode-ferroelectric structure, incomplete compensation of the ferroelectric polarization charge results when the center of gravity of this charge and the free compensation charge are not coincident. Depolarization fields in the ferroelectric arising from such incomplete compensations are estimated. A simple switching calculation shows such fields to be of sufficient strength to account for the initial polarization decay rate observed in Pb_0.92Bi_0.07La_0.01 (Fe_0.405Nb_0.325Zr_0.27)O₃ films. The results of measurements involving changes in film thickness, electron concentration in the electrodes, and contact materials will be discussed and shown to be consistent with the mechanism proposed.