Soft error in MOS dynamic RAM

Analytical and experimental studies are conducted on the soft errors of 64-Kbit dynamic RAMs. The critical charge, which is an important factor in soft errors of the device itself, is discussed, and the relation between the soft error rate and the critical charge is studied, comparing the supply voltage dependence of the soft error rate with experimental results. If the charge distribution collected in the silicon substrate is Gaussian, the soft error rate is expressed as a complementary error function of the critical charge and agrees well with experimental results obtained with Am-241. The dispersion is found to be 0.037 pC. Study of the Hi-C cell structure, boosted word line voltage, and polysilicon bit line showed that the critical charge is increased by a factor of 1.8 and the collection area is reduced to less than one half of the conventional case. The soft error rate is increased by a factor of 700.