Dielectric Properties And Molecular Simulation Of Polyimide/Silicon Nitride Films

As a functional material,polyimide?PI?has good dielectric properties,mechanical properties and chemical stability under high temperature and high electric field,and is widely used in military,aerospace,automotive electronics,microelectronics and other fields.With the development of science and technology,the thermal stability and dielectric properties of pure polyimide cannot meet the market demand.Therefore,it is widely expected that nano-filler can improve the performance of polyimide films.Ceramic materials are widely concerned because of their high thermal stability and low dielectric constant.Therefore,the doping of inorganic ceramic particles into polyimide has become a current research focus.Polyimide/silicon nitride?PI/Si₃N₄?composite films with different doping concentrations were prepared by in-situ polymerization.The relations between packing concentration and dielectric constant,dielectric loss and breakdown field strength were studied systematically.The results show that the 3 wt.%doped composite films exhibit excellent dielectric properties,with a dielectric constant of3.62,a dielectric loss of 0.038,and a dielectric strength of 237.42 MV/m.The increase of Si₃N₄doping will form an interface layer in PI,resulting in a large amount of space charge polarization under the action of electric field.The space charge characteristics of thin films were observed by PEA apparatus.The results show that the trapped energy level in the polymer can be used as carrier complex center and transport channel,which can effectively improve the insulation performance of the film when a small amount of filler is doped.The model of Si₃N₄,PI and PI/Si₃N₄was built by using Materials studio software,and the electronic structure and optical structure of the model were calculated by Castep,DMol3,Forcite and other modules.The bonding situation of each atom of Si₃N₄was studied,and it was found that bonding mainly consisted of p orbitals of Si and N.The energy gap is about 3 e V,and the dielectric constant at low frequencies is about 4 e V.We found that the highest electron occupied orbitals of PI are on the benzene ring,and the lowest electron occupied orbitals are on the imine ring.Bonding is mainly made up of p orbitals of C and O.Its energy gap is about 2e V.By calculating the dielectric function spectrum,the low-frequency dielectric constant is slightly lower than 3,which is the same as the actual situation.The surface interaction energy of PI and Si₃N₄particles was calculated by using the molecular dynamics theory,and the change of surface interaction energy of PI and Si₃N₄particles with the radius of Si₃N₄was studied.The effect of van der Waals forces caused by particle size on the interface region is discussed.