The effect of surface layer on the dielectric behavior of complex oxide thin films

Complex oxide thin films, such as ferroelectric thin films, are widely used in various devices. However, the chemical composition and chemical bonding of the surface layer are usually different from those in the ‘bulk’ region of the oxide thin films. The existence of the surface layer will certainly affect the properties, such as the dielectric behavior, of the films. In this paper, a model for evaluating the effect of the surface layer on the dielectric behavior of oxide films is proposed. The effective dielectric constant of the thin films is suggested as a function of the dielectric constants of expected and unexpected compounds in the surface layer, the content of unexpected compounds in the surface layer, and the volume fraction of the surface layer in the whole thin film. As an example, the dependence of the effective dielectric behavior of PbTiO3 thin films on the surface layer has been estimated using this model. The results show that a surface layer deviating from the stoichiometry of the film has a pronounced effect on the effective dielectric constant of thin films. It is obvious that in the design of oxide films and film devices the effect of the surface layer on the dielectric behavior of the films should be taken into account.