Investigation of charge trapping in thin Kapton® polyimide films by means of photo-stimulated discharge spectroscopy

Photo-stimulated discharge-current spectroscopy was performed on 50 μm Kapton® 200HN polyimide thermo- and photoelectrets formed in the temperature range between -40°C and +130°C. Films were either charged in the DC electric field of 20 MV/m or photo-charged by illumination with light at the wavelength of 420 nm under the electric field of the same strength. Photocurrent spectra scanned in the wavelength interval 600-350 nm demonstrate a pronounced peak at approximately 470 nm revealing the presence of one charge-trapping level. The long-wavelength cut-off of the peak is at 550 nm corresponding to 2.3 eV trap depth.