Quantum chemical calculation studies on hetero charge accumulation in polyimide film containing water

A large quantity of hetero charge was observed in polyimide (Kapton^®-H) film subjected to high electrical stress of 100kV/mm and under the condition of high humidity. In order to investigate the hetero charge accumulation, Quantum Chemical Calculation was applied to a small piece of polyimide specimen for obtaining an energy band structure, a band gap and an electric carrier trap level. Furthermore, it is discussed that a dipole moment of a series of water molecules made a narrow band gap in the polyimide chain, which increased more hetero charge, and finally led to a thermal breakdown by increasing conductivity.