Total-Dose Failure Mechanisms of Integrated Circuits in Laboratory and Space Environments

Total-dose failure mechanisms are identified over a wide range of dose rate for 2K and 16K SRAMs from hardened and commercial CMOS technologies. Failure was defined "parametrically," such that an IC fails if one of its parameters, e.g., static power supply current or timing, exceeds a preset specification following irradiation. These studies demonstrate that the dominant failure mechanisms of SRAMs in space radiation environments are often quite different than those observed at considerably higher laboratory dose rates specified by DoD test guidelines, i.e., 100 to 300 rad(Si)/s. In addition, the total-dose hardness of SRAMs varied significantly between laboratory and space dose rates. Several approaches are discussed for predicting total-dose hardness of ICs in space from laboratory measurements. Results are also presented for transistors irradiated over the same range of dose rate (200 to 0.02 rad(Si)/s) and at all biases, i.e., N-on/off and P-on/off. These transistor measurements are used to characterize the physical mechanisms that govern the radiation response of the more complex SRAMs. In a surprising result, a dose-rate dependence for the buildup of radiation-induced interface states was observed. At dose rates from 200 to 0.02 rad(Si)/s, the number of interface states at a given total dose increased as the dose rate decreased.