Transient Response of MOS Transistors and Integrated Circuits to Ionizing Radiation

Abstract

The following conclusions have been obtained from a study of transient radiation effects phenomena on MOS transistors and integrated circuits. The dominant response mechanisms for Sprague MOS transistors packaged in nitrogen encapsulated TO-5 cans have been identified as: radiation induced leakage from. a lead to the case due to ionization of the encapsulated gas, and the primary photocurrent of the drain-substrate p-n junction. The ionization-induced leakage can be reduced considerably by using air or paraffin as an encapsulant or by using a smaller package. For Sprague p-enhancement transistors, the two identified mechanisms are sufficient to explain all observed responses at various load and bias conditions. For Sprague n-depletion transistors, however, additional response mechanisms must yet be identified to fully explain the observed response. The additional response mechanism(s) is believed to be associated with carrier generation in the channel region and, in the active region, the additional drain current can be explained as a transient change in the threshold voltage (VT) of the device. The MOS digital integrated circuits which were tested exhibited transient radiation failure thresholds on the order of 10 to 100 r for radiation pulse widths less than the RC time constants of the circuits (typically, ?sec). Both substrate photocurrents and the gm amplification of induced gate voltage changes are instrum. ental in causing failure in microcircuits. No latch-up phenom. ena were observed in any of the microcircuits tested.