Résumé
The work is performed to investigate the electrical properties of multi-structure polyimide (PI) films, such as space charge phenomenon that can help us to improve the performance of these insulating films. Under high electric field and temperature, some changes at the atomic scale can lead to the space charge accumulation. Thermal Step Method (TSM) is a sensitive and handy technique to observe such changes in dielectric materials. It is used to observe the ability of these multi-structure films to accumulate/release space charges after thermoelectric poling, close to the practical applications. In-Situ polymerization method is used to prepare PI films. After curing, some films were fluorinated and put under electric field for different temperatures. Thermal Step (TS) current is measured using current amplifier and then space charge density and electric field can be calculated mathematically. From results, we found that the TS current for fluorinated films is quite different from non-fluorinated films. Coating of fluorination on both sides act as barrier and provide resistance to space charge injection from the electrodes. These coated-layers are discharge resistive and increase the charge dissipation rate to limit the space charge accumulation.