Depletion region geometry analysis applied to single event sensitivity

The effects of device geometry on single-event-upset (SEU) rate in space, beginning with the ground test measurements, are explored. Analysis of sensitive volume geometry is used to establish a relationship between it and SEU cross section. This relationship is used as a basis for geometric models wherein measured cross sections determine model shape parameters. Fits of one of these models to a range of experimental cross sections are exhibited. These fits and physical argument suggest that the actual sensitive volume shape differs from that assumed in most current calculations, i.e. a rounded shape with no lower corners is more appropriate than the box shape currently used. A correction that justifies a current heuristic practice of relating critical charge to an LET (linear energy transfer) on the shoulder of the cross section rather than to onset LET is devised. A further correction is obtained by a calculation using the omnidirectional chord distribution for a hemisphere. Together the two corrections show that nearly an order of magnitude error results from assuming that the sensitive volume is box shaped when calculating upset rate due to isotropic fluences