An Analytical Method for Predicting CMOS SRAM Upsets with Application to Asymmetrical Memory Cells

An analytical method was developed to predict the heavy-ion-induced upset rate of static random access memory (SRAM) cells. The method was applied to the design of a memory with asymmetrical cells where the goal was to increase the upset rate in order to increase the number of observed upsets in a space environment. The asymmetry is achieved by increasing the drain area of selected transistors in the cell. Results from the analytical model for a space environment indicate the upset rate for the experimental asymmetrical cell (17.2 upsets/l kbit-year) will be 4.7 times larger than the upset rate for the minimum-geometry balanced cell (3.6 upsets/ 1 kbit-year). The asymmetrical SRAM was designed into a test chip intended for the Combined Release and Radiation Effects Satellite (CRRES).