Preparation and characterization of low-permittivity polyimide-based composite membrane

Ultra-low permittivity (κ) materials have broad application prospects in the microelectronic fields. In this study, we prepared microporous polyimide-based composite membranes with ultra-low permittivity by incorporating a trace of cage-like Phenyl-POSS (POSS) into fluorinated polyamic acid (PAA).The effects of POSS incorporation on their dielectric properties correlated with the characteristics of the free volume defects of composite membranes have been investigated by positron annihilation technique. Incorporating POSS with hollow core into PI can effectively improve the free volume size and the relative volume fraction of composite membranes, which optimizes their low dielectric properties, but reduces their dielectric breakdown strength. The membrane with 3wt% POSS presents an ultra-low permittivity (κ = 1.77 at 10⁴ Hz) and maintains excellent mechanical properties. As POSS-doping amount reaches 5wt%, POSS agglomerates in composite membranes, resulting in a rebound in its permittivity. The incorporation of POSS reduces the tensile strength of composite membranes, which can be attributed to the fact that the rigid phenyl-POSS dispersing in the matrix weakens the interaction between the molecular chains of PI. The experimental results can provide valuable information for improving the dielectric properties of polyimide-based membranes in future.