Dielectric properties and relaxation behavior of polymethylsiloxane-imide films

We have investigated the dielectric properties, dielectric relaxation behavior, electric conduction and kinetic characteristics of polysiloxane-imide films. The addition of siloxane is a very effective way to reduce the dielectric constant (ε′) of polyimides. For example, polysiloxane-imide [BPDA + siloxane] has a very low dielectric constant of 2.66, compared to normal polyimides such as Upilex-S [BPDA + p-PDA] with a dielectric constant of 3.47. The dielectric relaxation behavior of polysiloxane-imide is quite similar to that of fluorine-containing polysiloxane-imide. As frequency increases, the transition peaks of polysiloxane-imide move toward high temperature and the α relaxation strengths decrease. The β peak corresponds to the β dipolar relaxation whereas the α peak is due to the conductive effects in the bulk and the α dipolar relaxation. The activation energy of the α transition decreases with increasing frequency, while the activation energy of the β transition does not vary with frequency. The α peak is reduced with the increase of frequency, while the value of the β peak hardly changes with frequency.