Characteristics of surface charges on corona-resistant polyimide films

In order to study the generating and decaying rule and mechanism of surface charges on the insulated films on micro/nano scale, electrostatic force microscope (EFM) was applied to investigate the origin and decay properties of surface charges on two kinds of polyimide (PI) films. Charges were injected onto the surface of the polyimide films using the conductive probe of EFM and the charges generated were characterized by EFM in situ, results of which indicate that the charges on original (100 HN) and corona-resistant (100 CR) polyimide films have different origin and decay properties. The injected surface charges onto the corona-resistant polyimide films were fewer and decayed quicker after injection, which was in accordance with the exponential rule and had the time constant of 19.9 min. The injected charges onto the original films were more, with the time constant of 48.1 min. Analysis shows that the addition of Al ₂O ₃ particles to the corona-resistant films effectively increases the dielectric constant and decreases the resistivity of the material. It is difficult to inject charges into 100 CR for Schottky effect between metal and dielectric, and the smaller decay time constant corresponds to the decrease of resistivity.