Relationship between breakdown and space charge formation in polyimide film under dc high stress

Relationship between breakdown strength and space charge formation in polyimide film under dc high stress at various temperatures is investigated using pulsed electro-acoustic (PEA) method. Polyimide films are used for various electric and electronic devices as insulating materials. They are demanded to show a good performance at various condition like at high temperature, under high electric stress with high humidity. Furthermore, since the material is expected to be much thinner, the breakdown characteristic is one of important factors to estimate the material. On the other hand, the space charge formation sometimes strongly affects to dc breakdown strength. Therefore, we have been investigating the relationship between the breakdown and space charge formation in polyimide film. It is found that hetero space charges are always found before breakdown. Since it is always observed before breakdown at high temperature, it may be predictive information for breakdown.