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 −40ºC and +130ºC. 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.
Observation of charge compensated polarization zones in polyvinylindenfluoride (PVDF) films by piezoelectric acoustic step wave response
A high resolution (2 μm) acoustic step-wave probing techniques has been developed to investigate the inhomogeneous distribution of the piezoelectric response of incompletely corona poled 85 μm thick PVDF films. We observe persistent polarization zones or layers of 20–40 μm width within the films which are electrostatically compensated by charge accumulation at the polarization zone boundaries. The zone development is explained by charge-trapping in proportion to polarization.
Pyroelectric transient response of polyvinylidene fluoride
The pyroelectric responses of conventionally poled films of polyvinylidene fluoride to a step input of radiation have been analyzed and shown to be well described by the superposition of two decaying exponentials governed by the thermal and the electrical time constants of the system respectively. The peak response of the pyroelectric current transient was observed to be proportional to both the pyroelectric coefficient d31 for PVF2 films of 25 μm thickness so that the peak current response curve may be used to evaluate p (T) and d31.