Enhancement of Dielectric Breakdown Strength and Its Possible Mechanism in Triple-Layered Films Formed by Stacking Resin Layers with Different Relative Dielectric Constants

Dielectric properties of co-extruded triple-layered films consisting of polymethyl methacrylate (PMMA) sandwiched between polyvinylidene fluoride (PVDF) layers were evaluated. The triple-layered films showed a higher dielectric breakdown strength and a higher energy density than each single-layer film, and the enhancement depended on the volume ratio of the PMMA layer, which has a lower relative dielectric constant than PVDF. The simulation of dielectric breakdown paths using the phase-field model revealed that the middle layer with a lower dielectric constant shares a higher voltage until its dielectric breakdown, resulting in an enhancement of the dielectric breakdown strength in the triple-layered film. The simulation results well matched the experimental data, indicating that controlling the volume ratio and relative dielectric constant of each layer in the triple-layered film is an effective approach to enhancing dielectric breakdown strength. This concept is considered promising for developing dielectric materials that enable a size reduction of film capacitors. A triple-layered film, in which a layer with a low relative dielectric constant (εr) is sandwiched between layers with a high εr, exhibited a higher dielectric breakdown strength (Ebd) than each single-layer film, and the enhancement depended only on the volume ratio of the middle layer. The phase-field simulation results of the dielectric breakdown paths explained well the experimental data.