Assessment of gated sweep technique for total dose and dose rate analysis in bipolar oxides

The efficacy of a gate sweep characterization technique for extracting radiation defect densities in bipolar devices as a function of total dose, dose rate, irradiation bias and device geometry has been studied. The parts analyzed were all NP type gated diodes formed with the n-type emitter and p-type base of a standard linear bipolar process. Diodes, having either 7 or 14 μm gate widths, were exposed to ionizing radiation at dose rates of 17 and 0.017 rad(Si)/s with either 0 or 10 V gate biases. Characteristics at several doses were measured using a step stress approach. The majority of the experimental results are shown to be consistent with the space charge model for enhanced- low-dose-rate sensitivity (ELDRS) in bipolar technologies. The results also show, as expected, that gate width has no influence on fixed oxide trapped charge buildup. However, the results suggest the need to refine the standard technique for extracting interface trap densities; where the area of the gate electrode is a critical parameter.