Soft errors in dynamic random access memories - a basis for dosimetry

The soft error rates of a number of 64k and 256k dRAMs from several manufacturers have been measured, employing a MC 68000 microprocessor. For this 'accelerated test' procedure, a 37 kBq (1 μCi)241Am alpha emitting source was used. Both 64k and 256k devices exhibited widely differing error rates. It was generally observed that the spread of errors over a particular device/manufacturer was much smaller than the differences between device families and manufacturers. Bit line errors formed a significant part of the total for 64k dRAMs, whereas in 256k dRAMs cell errors dominated; the latter also showed an enhanced sensitivity to integrated dose leading to total failure, and a time-dependent recovery. Although several theoretical models explain soft error mechanisms and predict responses which are compatible with our experimental results, it is considered that microdosimetric and track structure methods should be applied to the problem for its better appreciation. Finally, attention is drawn to the need for further studies of dRAMs, with a view to their use as digital dosemeters. (author)