Emerging ionic liquid-induced porous polyimide films toward ultralow permittivity, improved hydrophobic and electromagnetic wave absorption

There is an urgent need for interlayer dielectric materials with ultralow dielectric properties, high temperature resistance and hydrophobicity in the field of microelectronics due to the development of high-density integration and miniaturization of electronic components. Herein, porous polyimide (PI) films were successfully prepared by using ionic liquid (1-Butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4]) as porogen for the first time. Based on the inherent good compatibility between [BMIM][[BF4] and polyimide, this ionic liquid could be uniformly dispersed in the PI matrix, thus creating a favorable prerequisite for the formation of pores. It was demonstrated that the optimized rearrangement of PI molecular chains induced by etching process of [BMIM][BF4] led to the generation of pores and the reduction of chain spacing, which endow the porous films excellent dielectric, thermal and mechanical properties. The film with the porosity ratio of 85 vol% exhibited minimum permittivity of 1.5 at a wide range from 102 to 106 Hz, high temperature of 5% weight loss about 532 °C. The porous PI films not only provide the promising ultralow permittivity dielectric materials for the development of modern integrated circuits, but also present potential application in adsorption separation and special electromagnetic detection.