Polarization currents and switching in undoped poly-p-phenylene sulfide

Abstract

Charging and discharging electrical currents have been measured at room temperature in undoped PPS, with bimetalized aluminum electrodes. Sample thickness and area around 1 mm and 2.4 cm 2 respectively. Two regimes are observed. In the low voltage one the currents seems to result from the processes: dipolar polar i zation, and conduction caused by negative (electron) charge injection. From the transients we barely deduced the negative carrier mobility to be of the order of 10 −6cm 2/Vsec. These conclusions could be reached analysing the results obtained when one side metalized 25 μm thick teflon foil makes contact with an one side metalized PPS sample, allowing the formation of Maxwell-Wagner polarization. Both polarities were used in this study. A switching is observed for fields higher than 4×10 4V/cm and the current shows a large initial spike lasting a few seconds at this threshold, and less for higher fields, after which a steady state is reached. We have interpreted this behavior by an abrupt increase of free carriers at the threshold voltage. In this view, the current decreases because the bulk delivers more current than the contact may supply, forming a positive depletion layer. At more higher voltages the contact current increases faster and a space charge limit regime is observed.