Preparation And Properties Of Polyimide-based Composite Films With Low Dielectric Constant

The exploration of interlayer materials with low dielectric constant(low-k)is becoming urgent for reducing the increased impact of resistance-capacitance(RC)time delays,signal crosstalk and power consumption caused by the high integration and the reduction in feature size in the microelectronics industry.Polyimide(PI)is widely used as the flexible dielectric material because of its excellent electrical insulation property(dielectric constant ? 3.0 ~ 4.0,dielectric loss ? 0.02),mechanical property and good heat resistance.However,a lower dielectric constant is needed for the upcoming demands by the high integration in the industry.With the aim at developing PI films with lower dielectric constant,in this study,the relationship between different polymerization unit structures and the PI properties was explored first.After that,the PI with best performance among them was selected for the preparation of N,N '-Dimethylformamide(DMF)solvent soluble PI powder by chemical imidzation process,followed by the introduction of ZIF-8 nanoparticles for the preparation of a lower dielectric constant composite film.Zeolite imidazole framework compound 8(ZIF-8)has a high porosity,good stability and good compatibility with organics as well as the excellent hydrophobicity.So it can introduce nanopores and air into the polymer to reduce the dielectric constant of the material.Besides the dielectric properties,the moisture absorption and mechanical properties of the composite films were all studied systematically.The specific research contents are as follows:2,2'-Bis(trifluoromethyl)benzidine(TFMB),4,4'-Oxydianiline(ODA),4,4'-Oxydiphthalic anhydride(ODPA),3,3',4,4'-Benzophenonetetracarboxylic dianhydride(BTDA)were chosen for the synthesis of PI films(TFMB-BTDA,ODA-BTDA,TFMB-ODPA,ODA-ODPA),under the same conditions,for the exploration on the influence of different polymerization unit structures in the main chain of PIs on the performance.Based on the characterization of the performance of these 4 types PIs,the results showed that the dielectric constant of PI films decreased obviously with the introduction of bulk side groups,the increase of the flexibility of the main chain as well as the decrease of polar groups in the main chain.And the tensile strength of PI films decreased with the introduction of large-volume pendant groups,the decrease of polar group and the increasing flexibility of the main chain.Among them,the dielectric constant of PI(TFMB-ODPA)is 2.85 at 1MHz which is 4.40% lower than that of ODAODPA because of the introduction of bulky side groups,and the tensile strength of TFMB-ODPA is 81.9 MPa which is 8.2% lower than 89.2 MPa of TFMB-BTDA because of the increased flexibility and decrease of polar groups in the main chain.Based on the results above,TFMB-ODPA was selected owing to its good dielectric performance for the preparation of DMF solvent soluble fluorine-containing polyimide(FPI)by chemical imidization process.ZIF-8 nanoparticles were introduced to FPI to prepare ZIF-8/FPI composite films.The effects of ZIF-8 contents on the dielectric and water absorption properties were studied.The results show that the introduction of ZIF-8 nanoparticles can further reduce the dielectric constant of the composites and improve its mechanical property and hydrophobicity.The lowest dielectric constant of the composite films is 2.34(10 MHz)by incorporating 20 wt% ZIF-8(17.9% lower than that of pure FPI films),and the dielectric loss of composite films also decreased.The incorporation of ZIF-8 nanoparticles improved the hydroscopicity and mechanical properties of the composites as well.When the content of ZIF-8 was 20 wt%,the water absorption rate of the composite was 0.53%(41.2% lower than that of pure FPI film),and the young's modulus reached 3.23 GPa(88.6% higher than that of pure FPI film).