Radiation Induced Latch-Up Modeling of CMOS IC´s

The basic mechanisms of radiation induced latch-up in bulk CMOS IC´s have been relatively well understood for quite a while. There have been a number of attempts to quantitatively model these mechanisms and, to a first order, these have been quite successful. However, the ability to take into account second order effects such as conductivity modulation caused by electron-hole pair generation and two-dimensional effects has been lacking. This paper presents the result of applying a two dimensional, time variant, finite difference code (PISCES) to this class of problem. The results make it possible, for the first time, to quantify the effect of variables such as epi-layer thickness and device layout on the initiation of latch-up. In addition, it has been found that even if latch-up is precluded, the gain of the npn transistor multiplies the effect of the photocurrents such that the onset of rail span collapse induced errors will be accelerated.