Suppression of Size Effects in Ferroelectric Films

TL;DR: In this paper, the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films and two extreme boundary conditions are taken to prove their point.

Abstract: It is widely reported that the dielectric permittivity of ferroelectric films decreases with decreasing film thickness, and understanding and controlling these size effects are very important for charge storage application of these films. By combining phenomenological theory with careful experimental work, we have shown that the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films. We have taken two extreme boundary conditions to prove our point. For the case normal electrodes, it is assumed that the boundary condition for the component of polarization vector at the ferroelectric/electrode interface is P = 0. This case corresponds to the presence of a strong edge field, resulting in “freezing out” of the ferroelectric polarization at the interface and thus exhibiting severe size effects. However, if one utilizesconductive oxide electrodes that are ferroelectric in nature the polarization would not vanish at the ferroelectric/electrode interface and therefore the size effects are largely suppressed. To prove our point and to eliminate grain size, stress, and compositional effects, epitaxial SrTiO3 thin films with stoichiometric composition on SrTiO3 single crystal substrates were investigated. In fact, the experimental data also indicates that the use of ferroelectric electrodes indeed suppress the size effects.