Space charge in polyimide film exposed to high-dose electron beam

Polyimide film has no softening point below a temperature of 500°C and it has excellent mechanical characteristics in the range from the temperature of liquid helium to 500°C. It is thus considered one of the best heat-resistant macro-molecules. It is also highly resistant to radioactivity, such as beta and gamma rays, as well as to chemicals. Thus it is expected that polyimide film will be adopted as an electrical insulating material for use in severe environments. There have been many reports on the dielectric, electroconductive and dielectric breakdown characteristics of polyimide. However. there has been little consideration of space charge, which may have an adverse effect on electrical insulating property. This study investigated the changes over time in space charge density and its distribution after a bias voltage was applied to polyimide films with or without application of a high-dose electron beam