The Research Of Electronic Structure And Breakdown Mechanism Of PI/SiO₂

As a kind of functional material, PI has excellent dielectricity and good mechanical property etc under high temperature, and it has been applied in the fields of space fight and microelectronics. PI hybrided by nano-particles is the hotspot of recent research, and its corona-resistance life is 500 times more than PI's, and it has been applied widely in the frequency control technology systems. But the breakdown mechanism and the nano-particles's functions in the process of breakdown are unknown.The geometrical and electronic structure of PI and PI/SiO2 are simulated using MS 3.0. The simulation results indicate that the geometrical structures of middle fragment of PI (n=2, 3, 4) are consistent, and using structure of middle fragment of low polymer to describe the structure of high polymer is feasible. The bond orders among atoms of PI are gained by Mulliken method, and the bond order of C(7)-O(8) is stronger, the bond orders of O(1)-C(2), C(5)-N(6), N(6)-C(7) and C(7)-C(9) are inferior to others. Nano-particles of SiO2 form the hydrogen bond with carbonyl of PI, which changes the geometrical and electronic structure of PI, but the bond order changes a little.The films of PI/SiO2 and PI, which produced by ourselves, are made to break down under high electric field, and the surface defeature of films and the microstructure of the shot hole are studied using SEM. The testing results show that the breakdown field strength of PI/SiO2 and PI are 195.8KV/mm and 181.82KV/mm respectively, and nano-hybridization improves the electricity resistance character of the PI film. The film of PI/SiO2 is destroyed on the edge of the shot hole; there are a lot of small holes and discharge trace near the shot hole. And a large range of the surface near the shot hole of PI is protuberant, and the badly destroyed filed spreads about 100μm far away from the shot hole. The material near the shot hole becomes coarseness and appears molten. The...