Materials and Design 24 (2003) 377–382 0261-3069/03/$ - see front matter  2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0261-3069(03)00030-X The effect of surface layer on the dielectric behavior of complex oxide thin films Dingquan Xiao*, Linli Meng, Guanglong Yu Department of Materials Science, Sichuan University, Chengdu 610064, PR China Received 21 September 2002; accepted 7 February 2003 Abstract 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 PbTiO thin films on the surface layer 3 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.  2003 Elsevier Science Ltd. All rights reserved. Keywords: Films and sheets; Electrical; Engineering design; Conceptual design; Ferroelectric thin film 1. Introduction In recent years, preparation of thin films for meeting various requirements of commercial and space devel- opments has become one of the fastest-growing areas of solid-state materials. The range of complex oxide thin films is enormous and embodies magnetic, supercon- ducting, dielectric, acoustic and optical thin-film com- ponents. For example, complex oxide ferroelectric thin films are widely used in various devices, including non- volatile ferroelectric thin-film memories, metal–ferroe- lectric–semiconductor field-effect transistors (MFSFETs) and related devices, tunable dielectric devices for broadband wireless communications, pyroe- lectric devices, devices for microelectromechanical sys- tems (MEMS), etc. w1x. However, the chemical composition and chemical bonding in the surface layer are usually different from those in the ‘bulk’ region of the complex oxide thin films, which has been widely reported in the literature. *Corresponding author. Tel.yfax: q86-28-85415045. E-mail address: nic0402@scu.edu.cn (D. Xiao). For example, different element enrichment of Pb, La or Ti was observed in the surface layer of (Pb,La)TiO 3 thin films w2–7x. The surface layer contains multicom- ponents other than the expected stoichiometric complex oxide. The existence of the surface layer will certainly affect the properties, such as the dielectric behavior, of the films. For a surface layer containing multicomponents, the effective dielectric constant can be predicted by dielec- tric mixing modeling. Many dielectric-constant mixing models have been proposed and they are generally divided into four broad categories: effective medium w8–11x; empirical and semi-empirical w12–15x; phenom- enological w16x; and volumetric w17x approaches. In this paper, we propose a numerical model using effective-medium theory to discuss the effect of the surface layer on the dielectric behavior of oxide films, since the effective-medium theory has succeeded in solving some problems similar to the one we discuss here. The effective dielectric constant can be predicted based on some specific measurable parameters using this model. The results show that deviation of the surface