Total Dose Effect on the Propagation of Single Event Transients in a CMOS Inverter String

Pulsed laser light has been used to reveal how total ionizing dose radiation affects the propagation of single event transients in a string of inverters. By holding the input to the string of inverters at high voltage (1.8 V) during exposure to ionizing radiation, an asymmetry in the threshold voltages of the n-channel transistors is induced, i.e., the inputs to the inverters alternate between high and low voltage, which results in every odd-numbered n-channel transistor experiencing more Total Ionizing Dose (TID) degradation than the even-numbered n-channel transistors. The asymmetry manifests itself as an additional broadening of laser-light induced transients when the input to the string of inverters is set to low voltage and a contraction of the transients when the input is set to high voltage. Exposure of the inverter string to heavy ions with a fixed input voltage resulted in a contraction of the transients, regardless of whether the input was at high or low voltage, behavior that is consistent with the results from pulsed laser testing.