Total-Ionizing-Dose Induced Timing Window Violations in CMOS Microcontrollers

The total-ionizing-dose robustness of low power microcontrollers is investigated. Experiments reveal that with increasing total ionizing dose (TID), the "Timing Window Violations," i.e., inability of the instruction set to execute within the clock-cycle(s) lead to failures in microcontroller operations. Clock frequency and supply voltage of the microcontroller are varied to determine the maximum clock frequency at which the microcontroller can execute software subroutines without failure. Low power microcontrollers from two different manufacturers were tested. The maximum clock frequency decreases with increasing TID for both parts. A model for the degradation based on analysis of circuit level timing models is presented. The microcontroller robustness implications for system designers and ASIC designers are discussed.