Processing enhanced SEU tolerance in high density SRAMs

The authors report theoretical calculations and experimental verification of an increase in memory cell SEU tolerance when Sandia's 2μm-technology 16K SRAMs are fabricated with a radiation-hardened 1μm CMOS process. An advanced 2D transient transport-plus-circuit simulator has been employed to calculate the differential contributions from each of the vertical dimensional changes in the transition from the 2-μm process to the 1-μm process. Error cross-section data, performed at the Berkeley cyclotron, on the first such device lot indicate that total improvement in threshold LET is a factor of 2 or better. A saturation phenomenon associated with the high-LET events is described and physical mechanisms responsible for the saturation are discussed