Biased-Irradiation Characteristics of the Floating Gate Switch in FPGA

The radiation characteristic of the floating-gate switch in a 0.22 mum flash-based FPGA is investigated by measuring the threshold voltage after each stage of X-ray irradiation. The focus is on the applied bias on the floating-gate device during irradiation. A two-parameter, semi-physical model is used to fit the experimental results. For an erase or write state with a particular irradiation-bias, a set of two fitting parameters can accurately determine the threshold voltage with respect to total radiation dose. The modeling result can be easily integrated into the SPICE simulator for circuit design purposes