Study on evolution of deep charge traps in polyimide irradiated by low-energy protons using photo-stimulated discharge technique

Abstract

In this paper, low-energy proton irradiation effects on the evolution of deep charge traps in proton pre-irradiated polyimide are investigated using the photo-stimulated discharge (PSD) technique. The results indicate that in the PSD spectrum there appear three discharge bands with some sub-peaks in the wavelength range from 250 to 300 nm, 300 to 325 nm and 325 to 350 nm, respectively. After proton irradiation, the positions of the PSD bands show almost no change, while the integral intensity of the main PSD band (300–325 nm) decreases drastically from the original 175 pC in the pristine polyimide to the lowest one at about 10 pC in the irradiated sample, when 60 keV proton fluence is 1 × 1014 p cm−2. However, the intensity shows a certain recovery to about 50 pC as 60 keV proton fluence increases further to 1 × 1016 p cm−2. Further analyses indicate that the evolution of the PSD intensity is dependent on the displacement effect induced by proton irradiation. Structural analyses show that the degradation of carbonyl group in polyimide is the main reason for the decrease in PSD intensity due to proton pre-irradiation.