Relaxation currents in poly-4-vinylphenol dielectrics: Trapping and macroscopic polarization

The trapping currents and the macroscopic polarization-depolarization currents were observed together for a series of on-off switching of O ₂ plasma-treated and UV-treated poly-4-vinylphenol (PVP) dielectrics mixed with methylated poly (melamine-co-formaldehyde) (MMF). Initially, both O₂ plasma and UV created trap states on the PVP surface; however, prolonged O₂ plasma or UV promoted cross-linking of the PVP (MMF 40 wt.%) dielectric, and reduced the macroscopic polarization. Filtering of PVP solutions was also helpful in reducing the polarization. The slowly decreasing currents were ascribed to the trapping and buildup of charged-traps at the interface of PVP and the electrode, and this impedes the injection of further charges from the contacts. The macroscopic depolarization was found to be reduced with increased cross-linking. It is suggested that the macroscopic polarization-depolarization currents may possibly be related to free ions from the remnant hydroxyl groups inside the leakage channels.