Asymmetric Ferroelectricity and Anomalous Current Conduction in Heteroepitaxial BaTiO₃ Thin Films

Abstract

Asymmetric ferroelectricity and conduction of anomalous leakage current were observed in heteroepitaxial BaTiO3 thin films grown by rf magnetron sputtering at 600° C on three different electrode/substrate combinations: SrRuO3/SrTiO3, Pt/MgO and Nb doped SrTiO3. The voltage shift of hysteresis loops of the capacitance was a linear function of the thickness of the BaTiO3 films and became as large as 10 V in the film with a thickness of 410 nm. The asymmetry did not disappear even after a heat treatment carried out at 800° C in air. On the other hand, a steep increase in the leakage current was observed in the heteroepitaxial films when a positive voltage was applied. The origin of both the asymmetric hysteresis and the anomalous conduction is discussed in terms of asymmetric crystal structure caused by misfit dislocations introduced in heteroepitaxial growth.

Fundamentals of flexoelectricity in solids

“…Though one may conceive of such a situation, the simplest scenario for a dislocation-assisted stress release implies the formation of a narrow substrate-adjacent layer, where the strain gradient is mainly localized [92]. As was suggested by Abe et al [68,69], such layers in ferroelectric thin films may serve as the origin of the imprint effect. A simple theory to this effect was offered by Tagantsev et al [70].…”

“…Majdoub et al [64] and Zhuo et al [65] modeled the 'dead layer' effect on ferroelectric thin films conditioned by flexoelectricity. Modeling of flexoelectricity-driven internal bias in thin films was offered by Catalan et al [66,67], while a scenario for the flexoelectricity-driven imprint was offered by Abe et al [68,69] and modeled by Tagantsev et al [70]. The continuumtheory analysis incorporating flexoelectricity identified some unexpected manifestations of this phenomenon.…”

“…According to Abe et al [68,69], the flexoelectric field can make this layer non-switchable. A schematic of a ferroelectric capacitor containing a ferroelectric film where such a non-switchable layer is formed is shown in figure 9.…”

Direct determination of the effect of strain on domain morphology in ferroelectric superlattices with scanning probe microscopy

“…The field is well below (10% to 30% of E c ) the expected coercive field for epitaxial films. [47][48][49][50] We do not determine the origin of the internal field, but the difference between compensation at the top and bottom of the film would cause such a field.…”

Dielectric properties of Ba0.6Sr0.4TiO3 thin films using Pb0.3Sr0.7TiO3 buffer layers

“…[22][23][24] Therefore, misfit dislocations and interfacial space charge also could cause the asymmetry of the C-V curve. 25 The dielectric constant of PST/BST/PST films changed by about 31.7% under a bias of 0.85 MV/ cm while that of the BST films changed by about 36% under the same applied dc field. In the case of a layer composite, e.g., passive layer at the ferroelectric-electrode interface, the tunability can be suppressed.…”