Field-effect trap-level-distribution model of dynamic random access memory data retention characteristics

Dynamic random access memory data retention characteristics were investigated as a function of operating voltage. Based on a statistical process, called the trap-level-distribution model, which was proposed in our previous report, we further assumed that the junction leakage current by Shockley-Read-Hall process is enhanced by an electric field through the trap-assisted-tunneling process. We incorporated into the model two processes that cause variation in the electric field at the traps; the variation of electric field itself and the spatial trap distribution. By comparing the Monte Carlo and analytical calculations with the experimental results, we found that the retention time distribution is not only caused by the energy level and spatial distributions of the traps, but by the space-charge-region field distribution among the cells. A possible origin of the field distribution is the variation of dopant profile among the junctions.