SPATIAL AND TEMPORAL DEPENDENCE OF SEU IN A 64K SRAM

A pulsed picosecond laser was used to measure the spatial and temporal dependence of single event upsets (SEUs) in a 64K SRAM (HM65642C) that was not hardened to SEU. Consistent and repeatable upset thresholds and latchup were measured when the light was focussed on the drains of the sensitive transistors. The SRAM's sensitivity to SEU was found to depend on the arrival time of the laser pulse relative to the time when the cell was addressed. Striking results were found when the light was focussed outside the sensitive drains. Whether an upset occurred depended on both the position of the laser spot and the information stored in the cell. Under certain conditions an ''upset window'' was observed. A single pulse of light incident on a particular cell produced upsets in surrounding cells depending on the data stored in those cells.