Facile strategy for low dielectric constant polyimide/silsesquioxane composite films: structural design inspired from nature

It is important for the development of high-performance dielectric materials to reduce the dielectric constant and water uptake simultaneously, with the maintenance of mechanical properties. Herein, sandwich-type composite film was prepared through coating the both sides of flat polyimide (PI) film with polyhedral oligomeric silsesquioxanes (POSS) contained hierarchical porous structure using the microemulsion method, in which water droplets were used as the template for patterned pores. Due to the introduction of two layers of hierarchical porous structure with patterned pores and POSS, the dielectric constant of PI film was significantly reduced, accompanied by the low dielectric loss. In addition, the water uptake was also greatly reduced, thus contributing to its excellent durability under high humidity. More importantly, even with the introduction of porous structure, the mechanical properties of PI film can still be maintained, or even improved by optimizing POSS content. Through varying the POSS content from 10 to 50%, low dielectric constant of 2.28–2.42, dielectric loss of 0.005–0.009, water uptake of 0.56–0.62%, increment of dielectric constant under high humidity of 1.19–2.35%, with 26–32%, 43–69%, 77–80% and 31–37% of reduction, respectively, compare to flat PI film were achieved. These results indicate the potential of our sandwich-type composite film as low dielectric material in microelectronics.