Analysis of SRAM neutron-induced errors based on the consideration of both charge-collection and parasitic-bipolar failure modes

This paper describes an investigation of the upsetting of values in cells hit by alpha particles or neutrons, in which the feedback operation of the cross-coupled inverter in SRAM is accurately modeled through simultaneous device and circuit simulation. We demonstrate, for the first time, the existence and mechanism of a new parasitic-bipolar-failure (PBF) mode. Accurate values of critical charge (Q/sub cg/) for failure are calculated for both this mode and the conventional charge-collection-failure (CCF) mode. We identify opposite behaviors of Q/sub cg/ for the CCF and PBF modes with respect to the amount of charge at the storage node (Q/sub node/). The results on critical charge are also used to predict the soft-error rate and the prediction agrees with the results of measurement to within 30%. Based on the results, we propose design techniques for reduced SER.