Simulation for risk assessment of diode single event burnout

Abstract

High voltage Schottky diodes, often used in DC-to-DC converters are susceptible to single event burnout (SEB) due to energetic particle strike, posing a concern for their use in space components. Prior to recent test reports, diode SEB had not been considered a risk to space programs despite the phenomenon having been studied in high power terrestrial PN diodes in the 1990s. Schottky diodes have been engineered to prevent premature breakdown under high reverse bias voltage and minimize leakage currents at the edge of the contact electrode. Graded passivation structures, p+ doped guard rings, and a metallization field plate and thick field oxide help to mitigate failures due to the high electric fields resulting from sharp edge effects at the contact electrode. Recent heavy ion strike data indicates a tendency to failure along the guard ring structure and an effective drop in failure rate of two orders of magnitude has been observed after protective masking of the diode edge that includes this area. Due to the lack of comprehensive test data and understanding of the exact physics of failure, SEB in Schottky diodes has an uncertain impact on reliability. Existing space contractor derating guidelines may already be sufficient to mitigate this failure but with an uncertain margin that could further depend on the diode type, design, and implementation. We investigate the observed preferential SEB through physics-based computer modeling using Silvaco TCAD. We perform transient electro-thermal simulations on three-dimensional structures derived from destructive physical analysis (DPA) of failed diodes and failure sites. This effort should better the understanding of the risk of diode SEB by coupling numerical modeling with direct observations of failure.