Ionizing Dose Rate Effects in Microprocessors

The total ionizing dose failure levels in microprocessors for various radiation pulse widths appear to be dose-rate dependent. This apparent dose rate effect is demonstrated by comparing the total dose failure levels for 150-ns and 1-μs pulses, and >5-s 60Co irradiation. All irradiations were done while the device was operating under normal bias. Total dose failure level data are presented for five types of microprocessors: RCA 1802, Motorola 6800, Intel 8080 and 8085, and AND 9080. Each type exhibited the same dose-rate effects. This dose-rate dependence is caused by the collapse of the electric field across the gate oxide during irradiation. Resulting failure levels for high dose-rate exposure of MOS devices then approach the total ionizing dose failure levels for unbiased MOS devices which are from 3 to 10 times higher than biased devices. This unbiasing is caused by the large power supply currents which flow during the radiation pulse. These currents are limited by package lead resistances, which in most cases protect the device from burnout.