Space charge effect in ultrathin ferroelectric films

Space charge influence on the depolarization field becomes pronounced in nano-scale ferroelectric films in static state. We have studied theoretically the ferroelectric, dielectric, and piezoelectric properties of ultrathin ferroelectric films with the consideration of influence from space charges, surface, incomplete screening, and misfit strain. It is found that space charges accumulated near the surface of the film can modify the depolarization field, which results an enhancement of the polarization in ultrathin films and a persisting polarization even below the critical thickness. The singularities of the dielectric constant and piezoelectric coefficient were all being rounded near the critical thickness. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704178]