Applicability of LET to single events in microelectronic structures

Linear energy transfer (LET) is often used as a single parameter to determine the energy deposited in a microelectronic structure by a single event. The accuracy of this assumption is examined for ranges of ion energies and volumes of silicon appropriate for modern microelectronics. It is shown to be accurate only under very restricted conditions. Significant differences arise because (1) LET is related to energy lost by the ion, not energy deposited in the volume; and (2) LET is an average value and does not account for statistical variations in energy deposition. Criteria are suggested for determining when factors other than LET should be considered, and new analytical approaches are presented to account for them. One implication of these results is that improvements can be made in space upset rate predictions by incorporating the new methods into currently used codes such as CREME and CRUP