Polyimide degradation induced by irradiation with N+ ions

Abstract

The samples of Upilex R polyimide (PI) were irradiated with 90 keV N+ ions to the fluences from 5 × 1014 to 2 × 1017 cm−2, and sheet resistance (Rs) and thermoelectric power (TEP) were measured in dependence on the ion fluence and the sample temperature. The Rs achieves its minimum for the ion fluence of 1 × 1017 cm−2, and from the measured temperature dependence of Rs it may be concluded that the ion beam modified PI exhibits semiconductor properties with charge transport governed by the variable range hopping mechanism. The measured TEP of the PI samples irradiated to the fluences above 1 × 1016 cm−2 is low (the order of μV/K). Such properties are typical for metals, and the conclusion is that the charge transport in the irradiated PI samples is contributed by the mechanisms which are characteristic for both semiconductors and metals. The role of conjugated double bonds was examined by measuring absorption UV-VIS spectra. The number of the conjugated double bonds correlates with observed Rs, and the width of the forbidden band, determined from UV-VIS spectra, is a decreasing function of the ion fluence.