Processing of dielectric nanocube 3D-assemblies and their high electrical properties for next-generation devices

Abstract

Nanocrystals have great potential to achieve extremely high electrical properties induced by their shapes, size, and facet surfaces. BaTiO3 nanocube (BT NC) 3D-assemblies with numerous interfaces and closely packed nanostructure are attracting as materials for next-generation dielectric devices due to their advantages for enhancing dielectric properties such as high packing density, high orientation, and interaction of the interfaces between the nanocubes. In this paper, we review our studies on the solution-based processing of BT NC 3D-assemblies and their high dielectric properties. BT NCs 15 nm in size have already been synthesized by the hydrothermal method with aqueous compounds and surfactants. As NCs were well-dispersed in non-polar organic solvent, BT NC 3D-assemblies were fabricated by a dip-coating process while controlling the up-stroke rate of the substrate and evaporation rate of the solvent. The capillary force generated through the dip-coating assisted in ordering the NCs. We also successfully fabricated micro-patterning of BT NC assemblies using polymeric micro-molds and removing them by a chemical wet process. This soft process has the great advantages of avoiding both etching damage occurring in the dry process and the clamping effect of substrate. The ordering and cubic shape of the BT NC 3D-assemblies were maintained under heat-treatment up to 900°C. The local strain at the BT NC interfaces was induced by epitaxial attachment with small angle tilting between neighboring NCs. The dielectric constant of the BT NC assembly heat-treated at 850°C achieved above 4000 with relatively low loss tangent below 7%. The local strain at the interfaces seemed to enhance the dielectric properties without the nanosize effect and thickness effect of dielectric materials.