In order to obtain thin film dielectric layers with very low dielectric constants for use in
microelectronic devices, polyimide nanofoamed films has been prepared from the polyimide
precursors (PMDA-ODA) and poly(ethylene oxide) (PEO) in N,N-dimethylacetamide. The
synthesization process included blending polyimide as the major phase with a minor phase of the
thermally labile PEO blocks. The foamed films were characterized by a variety of experiments
including TG and SEM, and the experimental results indicated that the labile PEO would undergo
oxidative thermolysis to release small moleculars from the matrix so as to leave voids into the
polyimide matrix. The dielectric properties of the films were studied over broad frequency ranges.
The dependences of dielectric constant on the PEO content in the films and frequency were
discussed. The films with a proper amount of PEO displayed relatively low dielectric constant
compared to the pure polyimide film. Thin film foams with high thermal stability and low dielectric
constants can be prepared using the approach.