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. BaTiO 3 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 solutionbased 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 heattreatment 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.

Manifestation of dipole-induced disorder in self-assembly of ferroelectric and ferromagnetic nanocubes

“…5 particle sizes) 89,90 . However, dense multilayered superlattice assemblies of BaTiO 3 nanocubes 29,84,[91][92][93] were also produced in some experiments, where the kinetic effects have been systematically controlled. The surface and inner structure were highly ordered with SC lattice and a packing fraction up to 90% 29,94 over a relatively large area of up to ∝ 10 µm 2 84,91,93,95 with thickness varying from several hundred nanometers 29,84,94 up to a ∝ 1 µm 95 (several examples are shown in Fig.…”

Coexistence of Flexo- and Ferro-Electric Effects in an Ordered Assembly of BaTiO3 Nanocubes

“…To develop thinner high-performance smartphones and wearable devices, such as eyeglass-type and wristwatch-type, miniaturization and improvement of the properties of dielectric devices such as multilayer ceramic capacitors (MLCCs) are required. An ordered assembly of BaTiO 3 nanocubes (nanocrystals) is a candidate as the main component of such devices [1][2][3][4][5][6][7][8][9][10]. The size of a BaTiO 3 nanocube is about 15 nm, which is much smaller than the typical BaTiO 3 -based particles of about 100 nm in diameter currently used in MLCCs [5,6,[11][12][13].…”

Stabilization of Size-Controlled BaTiO3 Nanocubes via Precise Solvothermal Crystal Growth and Their Anomalous Surface Compositional Reconstruction

“…The authors of previous studies have reported using platinum (Pt) 11 and palladium (Pd) 12 nanocubes as a base substance; however, the strain between the BaTiO 3 nanocubes led to a high dielectric constant in the densely assembled ceramic. 13 That is, BaTiO 3 nanocubes are necessary for the material design because of the surface properties of the particles. The synthesis of BaTiO 3 nanoparticles requires three key points: (1) a method to control the particle size because nanoscale materials are desirable as a consequence of their large specific surface area; (2) a method to control the particle shape because cubes are desirable as a consequence of the wide contract area between nanocubes; and (3) a method to control the particle surface as strain between nanocubes is desirable because it eliminates the need for a dispersant or surfactant.…”