Abstract
The measurement and interpretation of high-field thermally stimulated depolarization current (TSDC) of capacitor-grade biaxially oriented polypropylene (BOPP) films are investigated in order to facilitate the derivation of trap parameters. Two main relaxations associable with the glass transition and detrapping of space charge from deep traps are observed, and their dependence on the polarization/depolarization conditions are studied. The complex bipolar nature of the space charge relaxation makes the derivation of trap parameters challenging. Lastly, a brief attempt is made to correlate the TSDC features with morphology and other short-term dielectric properties.
Highlights
thermally stimulated depolarization current (TSDC) measurement is a useful technique for studying charge storage and decay processes in polymer thin films
Upon heating from −50 °C, each film exhibited a broad TSDC peak around 0 °C which is attributed to the gradual release of charge from shallow traps as the amorphous regions pass through the glass transition (α-relaxation)
Strong TSDC peaks were observed in the high temperature region at T >75 °C, with the peak maximum occurring in the 110–120 °C range
Summary
TSDC measurement is a useful technique for studying charge storage and decay processes in polymer thin films. A number of issues related to e.g. sample preparation, morphology, surface roughness, electrode–polymer interface as well as the sole analysis of the TSDC data itself make the measurement and interpretation of high-field TSDC of thin polymer films far from trivial. Various data analysis methods for extracting the charge trapping parameters from TSDC spectra (and the issues related to them) are reviewed, ranging from simple methods assuming single discrete relaxations to full-scale deconvolution of (quasi-) continuous trap bands by multi-peak fitting or other techniques. A brief attempt is made to correlate the TSDC features of various capacitor BOPP films (manufactured by both bubble and tenter processes) with their morphology and other short-term dielectric properties
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