Gamma radiation effects on polyimide-passivated n+p diodes

Abstract

Polyimide-passivated n + p silicon diodes were exposed to several levels of cobalt-60 radiation. Forward and reverse current-voltage characteristics were recorded both before and from 26 to 500 h after the gamma irradiation. Conduction in the forward direction decreased and the diode quality factor improved following irradiation and measurement at 48 h. An increase in reverse leakage current was observed at 26 h. At 48 h, the leakage current dropped below the pre-rad value. Measurements made at times in excess of 48 h fluctuated slightly with time after irradiation, but these fluctuations disappeared after 144 h. Junction breakdown voltage was unaffected by radiation. The effects of radiation on device characteristics are attributed to charge creation and trapping in the polyimide layer followed by charge relaxation with time after removal of the radiation source.