Nonlinear dielectric properties of polyimide in high AC electric field

The nonlinear dielectric properties of polyimide (PI) films, excited by high-intensity, AC electric fields, have been measured. This work highlights that nonlinear DC conduction is a component of the AC conductivity and dielectric loss response when surpassing a certain threshold field strength. An additional Poole-Frenkel polarization, induced by high-intensity, high-frequency fields, also contributes to the nonlinearity. This increases the dielectric losses through a charge de-trapping process, the so-called jacking-up effect. A novel expression that captures the large signal behavior of the complex permittivity is introduced using the Cole-Cole format. Finally, it is shown that the dielectric properties and power dissipation density in PI films remain fully linear and frequency-independent up to an AC electric field of E-PF similar to 100 V-rms/mu m and more conservatively below a threshold field of E-x similar to 45 V/mu m (i.e., end of the ohmic region). Consequently, polyimide-based insulated electronic devices that are designed to continuously operate below this threshold field (including both uniform and fringe fields) will remain immune to a frequency-dependent electrical aging. Their lifetime should not be affected in any way. (C) 2022 Author(s).

Automated summary

This study investigates the nonlinear dielectric properties of polyimide films under high-intensity AC electric fields. It is found that nonlinear DC conduction is a component of the AC conductivity and dielectric loss response when the field strength exceeds a certain threshold. The high-intensity, high-frequency fields induce additional Poole-Frenkel polarization, contributing to the nonlinearity. The study introduces a novel expression in the Cole-Cole format to capture the large signal behavior of the complex permittivity. Experimental results demonstrate that the dielectric properties and power dissipation density in polyimide films remain linear and frequency-independent below a threshold field. Therefore, polyimide-based insulated electronic devices designed to operate below this threshold field will not be affected by frequency-dependent electrical aging.