Trapping and Thermal Release of Irradiation Electrons from Polyethylene Terephthalate Films

Electron irradiation of capacitor-type structures consisting of polyethylene terephthalate films with thin aluminum electrodes can result in a net charge distribution in the dielectric region. Irradiating with a non-penetrating beam of electrons (10–20 keV) and a constant beam current density (5×10−8 A/cm2), the transfer of charge through an external circuit after ceasing the irradiation was correlated with the practical range of the primary electrons. Assuming that the irradiated volume of the polyethylene terephthalate contained a uniformly distributed space charge, the observed values of external charge transfer were used to obtain a minimum value for the trapped irradiation electron density. For the 14-keV irradiation with a practical range approximately one half the thickness of the sample, a value of 1.6×1015 electrons/cm3 was obtained. The corresponding internal electric field near the irradiated electrode was 2×105 V/cm.