Physical model of bit-to-bit variation in data retention time of DRAMs

The low power application of DRAMs requires longer data retention time. Since the p-n junction current leakage is the main cause of the cell capacitor discharge, the leakage should be minimized to meet the requirement. However, the leakage taking place in a small area varies from bit to bit. Therefore, it is necessary to clarify the mechanism of the variation for the leakage minimization. A physical model, based on newly obtained experimental results, is proposed wherein the leakage variation is mainly due to a variation of local electric field strength enhancement.