Space-charge profiles with high densities in uniform and nonuniform polymer dielectrics

Rather high space-charge densities were achieved in the bulk of several Teflon fluoropolymers by means of corona charging at an elevated temperature. The resulting electric-field distributions were probed with piezoelectrically generated pressure steps; this technique is particularly well suited for directly measuring spread space-charge distributions in the volume of thin polymer films. From the calibrated pressure-step results, it is possible to estimate space-charge and thus also filled-trap densities; maximum space-charge densities of 600 C/m ³ corresponding to filled-trap densities of almost 4×10 ¹⁵ cm^-3 were observed on Teflon PFA under the present charging and annealing conditions, while the maximum space-charge densities in the other two Teflon variants were smaller by a factor of up to three. Some typical recent results on positively and negatively corona-charged samples of the three Teflon polymers TFE, FEP, and PFA are presented together with results on two-layer samples consisting of one positively and one negatively charged film, which demonstrate that the charges in the volumes of the individual films are quite well preserved upon mechanical (and electrical) surface contact