Radiation Hardness of a High Speed ECL Microcircuit

Abstract

The results of gamma irradiation (both break-out transistors and complete microcircuits) lead us to conclude that circuits produced using this process are very tolerant to this type of hostile environment. This would indicate good surface passivation resulting in low surface leakage currents. The circuits are reasonably tolerant to neutron radiation. As expected, the transistor current gains are degraded. However, the circuits are still functional after exposure to 1 × 1015 n/cm2. The probable reasons for this tolerance are (1) the construction necessary to produce such high speed circuitry results in a very narrow base region with a small emitter-base depletion region and (2) Emitter Coupled Logic operates at higher currents (than TTL for example) and the gain is degraded less (relatively) at higher currents (and thus higher operating frequencies). The above conclusion regarding higher tolerance at higher frequency is true for ECL circuits in general and this differential configuration in particular. However, it is not valid for high-speed circuits in general. If transistors are switched at higher current levels for higher frequencies, they would probably be more tolerant to neutron radiation. Each high speed logic family will have to be evaluated on its own merits and for particular applications for use in radiation environments. Another result that would be desirable is the transient response of the complete microcircuit to ionizing radiation pulses.