Correlation of Radiation Effects in Transistors and Integrated Circuits

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Abstract
The effects of ionizing radiation on discrete MOS n- and p-channel transistors are correlated with performance degradation of CMOS integrated circuits. The individual components of radiation induced charge, oxide-trapped charge and interface-state charge, are separated using a subthreshold current technique. Processing splits and post-irradiation biased anneals are used to vary the ratio of oxide-trapped charge to interface-state charge. It is shown that the effective channel mobility depends to first order on the interface-state charge density. Static power supply current is correlated with the n-channel leakage at zero gate voltage while output drive currents are a function of both threshold voltage and channel mobility. Changes in propagation delay of signals through integrated circuits can be understood when both mobility and threshold voltage are considered as a function of the bias dependent charge buildup. A new transistor switching time figure of merit, t/C, which measures the drain to source drive over a full logic level voltage swing at the drain node, is introduced. This index is then shown to correlate with propagation delay in an IC. Finally, performance changes in an IC are modeled using only the measured buildup of oxide-trapped and interface-state charges from transistors as a function of radiation.

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