Nonlinear dielectric properties of polyimide in high AC electric field

Abstract

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 EPF ∼100 Vrms/μm and more conservatively below a threshold field of EX ∼45 V/μm (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.