Radiation Effects on Monolithic Silicon Integrated Circuits

Both the transient radiation response and the permanent radiation damage of thirty-four types of monolithic integrated digital circuits were measured and the critical radiation thresholds for circuit failure were determined. A theory for the transient radiation response of OFF-gates is derived on the basis of primary photocurrent in the collector-substrate junction of the output transistor. From this theory the critical radiation thresholds can be predicted for circuit failure, which is defined in terms of circuit noise margin. The effects of fan-out are included in this theory, but it is shown that fan-in has no effect on the response. The theory is used to explain the qualitative features of the experimental results. The basic features of the transient radiation response of ON-gates are also examined and analyzed. It is demonstrated that the sensitivity of ON-gates can be minimized by a proper choice of supply voltage and circuit design. A theory for permanent damage in monolithic integrated circuits is derived on the basis of existing theory of the degradation of current gain , E in trnsistors. From this theory the criticsl radiation threshold can be predicted for circuit failure which is defined in terms of the increase of the output voltage to levels above which noise margin disappears. This theory is in agreement with the experimentally observed results.