Overall improvement in dielectric and mechanical properties of porous graphene fluoroxide/polyimide nanocomposite films via bubble-stretching approach

Low dielectric constant is desired for polyimide to be used in microelectronic industry. In the present study, a series of porous graphene fluoroxide/polyimide (GFO/pPI) nanocomposite films with improved dielectric and mechanical properties were fabricated. Polyethylene glycol (PEG) was introduced into the system to play the roles of an intercalator in exfoliation of graphite fluoroxide and a blowing agent in preparation of porous structure. The in-situ bubble-stretching, resulting from PEG decomposition during the thermal imidization, not only hindered the agglomeration of GFO nanosheets, but also generated micro-pores in PI matrix. Both the porous structure and the GFO nanosheets significantly decreased the dielectric constant of composite films, and the load transfer between GFO and PI matrix efficiently improved the mechanical properties of composite films. A very low dielectric constant of 2.29 as well as high tensile modulus of 4.43 GPa and tensile strength of 159 MPa was obtained for the composite film with the GFO loading of only 0.30 wt%. In addition, the glass transition temperature of GFO/pPI films was increased from 355 °C to 388 °C, and the coefficient of linear thermal expansion of GFO/pPI films was decreased from 48.7 ppm/K to 24.9 ppm/K. Keywords: Polyimide, Graphene fluoroxide, Micropores, Dielectric property, Mechanical properties