Total Dose Effects on Circuit Speed Measurements

Measurements of propagation delay as a function of total ionizing dose were made using ring-oscillators, inverter chains, and NAND chains fabricated on the same CMOS test chip. The data illustrate the impact of the bias conditions of the MOS transistors during irradiation on the propagation delay time of the circuits. The data show no difference in propagation delay time for the three circuit types if comparable bias conditions are maintained during radiation exposure. The threshold voltage shift of the n-channel transistors appears to be the dominant factor controlling the decrease in propagation delay as the total dose increased. The ultimate failure of the test circuits is due to the shift of the n-channel transistors to a negative threshold voltage.