Field Grading Composites Tailored by Electrophoresis — Part 1: Principle and Permittivity Gradient in Uniform Electric Field

A series of three articles present an innovative way to build advanced functionally graded materials (FGM) based on polymer/ceramic composites tailored by electrophoresis from the process principle to their field grading application in power electronics. In this Part 1, the process is presented and relies on applying a DC voltage on liquid composite compound before curing in order to `freeze' the particles where they have been accumulated. To exemplify this principle, FGM composites involving an epoxy resin with SrTiO3 high-k particles with a permittivity gradient are presented. The methodology to build and characterize them is carried out. An accumulated particle region is observed at the high voltage electrode while the depleted bulk region remains unmodified. This accumulated particle layer both increases in thickness and in filler densification with increasing the field and/or time allowing tuning its permittivity. This work paves the way to the development of more robust electronic systems where the electrical fringe field in critical regions can be mitigated.