Charge accumulation, conduction mechanisms and degradation in high fields on PEN

The insulating polymers, used in a great number of applications in electrical engineering, are studied to learn about their behavior as they are conditioned under high electric fields. In that case, charge injection and electric conduction may cause a possible degradation of the material, electrical aging mechanisms, electroluminescence, and eventually an electronic and/or thermal breakdown. In order to study the origin of this behavior, we studied a 25 μm thick semicrystalline PEN (Polyethylene -2,6-Naphthalene Dicarboxylate) sample, close to pre-breakdown fields, i.e., 290 kVmm^-1. Several experiments were carried out, that allow us to improve a comparative study between the evolution of space charge profiles and isochronal characteristics J(F). The FLIMM method (Focused Laser Intensity Modulation Method) was used to get space charge profiles. This is a technique allowing the in-depth localization of charges and/or polarization within an insulator. Resulting from the superposition of the transient charging and discharging currents, the dipolar currents are identified and considered to play the main role among all phenomena involved in the field range up to 144 kVmm^-1. On the other hand, the induced space charge accumulation seems to give a really important indication of the triggering of the charge injection. They are dominant above a J(F) threshold field, and reveal a similar behavior to the classical J(F) characteristics.