Resistive switching phenomena in thin ferroelectric films

Switching of the resistance in thin ferroelectric films is a complex phenomenon involving an influence of polarization states, point defects, processes of electron injection from electrodes and peculiarity of polarization charges screening. In order to clarify the mechanism of surface charge screening under ferroelectric polarization switching and its correlation with the local resistive properties in thin ferroelectric films, we studied the changes in the surface potential under dc bias voltage application in SrTiO/LaSrMnO/BaTiO heterostructures using different modes of atomic force microscopy (Kelvin probe, piezoresponse, and conductive) at ambient conditions. It is found that the peculiarity of surface charge screening under polarization reversal gives a strong electrostatic contribution in the measurements of local resistive properties at the ambient conditions and could completely veil the real current distribution over the film surface. Remarkably, scanning tunnelling microscopy measurements under ultra-high vacuum conditions show evidence of oxygen vacancy formation in thin ferroelectric films after poling, revealing an increase of the film thickness due to the chemical expansion.