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 (epsilon') 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 a relaxation strengths decrease. The beta peak corresponds to the beta dipolar relaxation whereas the alpha peak is due to the conductive effects in the bulk and the a dipolar relaxation. The activation energy of the a transition decreases with increasing frequency, while the activation energy of the beta transition does not vary with frequency. The alpha peak is reduced with the increase of frequency, while the value of the beta peak hardly changes with frequency.