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U13.2.1

Microstructure and dielectric properties of epitaxial BaTiO3 films and BaTiO3/SrTiO3 multilayers A. Visinoiu, R. Scholz, M. Alexe, and D. Hesse Max Planck Institute of Microstructure Physics, D-06120 Halle (Saale), Germany. ABSTRACT Epitaxial BaTiO3 films and BaTiO3/SrTiO3 multilayers were grown by pulsed laser deposition (PLD) on (001)-oriented Nb-doped SrTiO3 (SrTiO3:Nb) substrates. Measurements of the dielectric properties were performed comparing BaTiO3 films and BaTiO3/SrTiO3 multilayers of different number of individual layers, but equal overall thickness. The dielectric loss saturates for a thickness above 300 nm, and linearly decreases with decreasing film thickness below a thickness of 75 nm, and it is independent on the number of multilayers, pointing to some interface effect. The thickness dependence of the dielectric constant of BaTiO3 films and BaTiO3/SrTiO3 multilayers exhibits a change in the linear slope at a thickness of 75 nm. This behavior is explained by the change observed in the morphology at a thickness of 75 nm. In order to explain the thickness dependence of the dielectric constant, two approaches are considered in this paper, viz. a “series capacitor” model and a “dead layer” model.

INTRODUCTION In order to explain the decrease in dielectric constant with film thickness various models have been proposed, viz. low dielectric constant space charge layers [1], oxygen depletion zones adjacent to metals with a high oxygen affinity [2], formation of surface states [2], local diffusion of electrode material into the ferroelectric [3,4], lattice mismatch induced ion vacancy formation [5], a chemically distinct surface phase [6], intrinsic surface polarization effects [7,8], depolarization fields due to incomplete screening by the electrodes [9,10], intrinsic suppression of polarization at the electrode [11], formation of a Schottky barrier and an associated depletion layer as a result of band bending at the ferroelectric-electrode interface [12]. Recently another model was proposed by assuming the existence of so-called “dead layers” at the electrodeferroelectric interfaces having a severely depressed dielectric constant. These interfacial dead layers act as parasitic capacitors in series [13] or in parallel [14] with the bulk-like ferroelectric. Two approaches are considered in this paper to explain the thickness dependence of the dielectric constant of BaTiO3 films and BaTiO3/SrTiO3 multilayers, the “series capacitor” model in case of thin films and the “dead layer” model in case of thick films with columnar structure.

EXPERIMENTAL DETAILS Epitaxial BaTiO3 films and BaTiO3/SrTiO3 multilayers were grown by PLD on SrTiO3:Nb (001). The deposition conditions, the morphology of the BaTiO3 thin films, and the microstructure of the BaTiO3/SrTiO3 interfaces are presented elsewhere [15,16]. Pt electrodes with a thickness of 100 nm and a diameter of 0.15 mm were deposited by rf sputtering through a

U13.2.2

metallic mask at room temperature. Electrical characterization was performed using a He