Application of a diffusion model to SEE cross sections of modern devices

A diffusion model, based on extensions of the analysis by Kirkpatrick (1979), appears to explain a number of ''anomalous'' features of the cross section measured as a function of the LET of the incident ions in some modern devices. In contrast, heuristic corrections are needed to fit the data with models based on drift of charge to and in a rectangular parallepiped. In particular the following features of the accelerator measurements are explained. (1) Cross sections at normal incidence much larger than the dimensions of depletion regions. (2) As the LET of the ion is increased above the onset threshold, the cross section increases gradually; it is not a step function. The cross section does not approach an asymptote, even at normal incidence. (3) There are discontinuities in the cross section versus effective LET when ion species are changed. (4) Cross section curves are approximated with Weibull distributions. The model is applicable when cross sections at large LET values are small (similar to 10 mu m(2)). A procedure for calculating upset rates is developed, although it is not implemented at this time. The model is preliminary. The ultimate limits of applicability and the transition to the standard rectangular parallepiped (RPP) model have yet to be established.