Injection of charge carriers and space charge build-up in fluoropolymer dielectrics

This study concerns the injection of charge carriers and space charge build-up in fluoropolymer films by the thermally stimulated discharge (TSD) current method. Poling fields ranging from 2.5 to 20 MV m^-1 are employed with the heating rates of 0.5-2 K min^-1 over the temperature range of 0-200°C for TSD experiments. Silver and aluminum electrodes are employed to study the role of the cathode in the injection mechanism. The TSD currents are observed to depend on the cathode material. The magnitude of current peak and the total charge released to the external circuit with both electrode materials show a saturating trend with the poling field. This observation is consistent with the suggested mechanism of charge injection from electrodes and the space charge build up in the material. Relaxation times in the range of 4-6000 s are observed over the temperature range. Mechanisms of space charge build-up are also discussed