A static RAM says goodbye to data errors [radiation induced soft errors]

The sensitivity of memory cells to soft errors is directly related to the cell´s capacitance: the smaller the capacitance, the greater the sensitivity. In concept, the approach taken by STMicroelectronics is a simple one. It is to add two extra capacitors to each memory cell. With capacitors, one on each side of the cell, which have a value of about 35 fF, much larger than that of the cell, it is made practically immune to soft errors. To save space, these capacitors were stacked on top of transistors. Under test, they found that the produced SRAM was completely immune to soft errors caused by alpha particles, and, when biased at 1.2 V, 250 times less sensitive than conventional SRAMs to soft errors from neutrons - a rate acceptable to the semiconductor industry.