High-Tc Superconductor-Insulator-Superconductor Heterostructures with Highly Resistive Insulator Layers

Trilayers in which a dielectric or ferroelectric film such as SrTiO(3), BaTiO(3) or Ba(x)Sr(1-x)TiO(3) separates two layers of a high-Tc superconductor are required for many device applications of high-Tc materials. To clarify the mechanism limiting the insulation properties of the insulating layer, the microstructure of such samples was analyzed using transmission electron microscopy. These studies suggest that diffusion along threading dislocations or along grain boundaries in the insulating layer lowers its resistivity. Substitution of the insulating monolayer with a bilayer to interrupt diffusion paths increases the resistivity of the structures to 3x10**13 Omega cm (at 2x10**5 V/cm, below 100 K).