VOLTAGE SHIFT EFFECT ON RETENTION FAILURE IN FERROELECTRIC MEMORIES

We investigated the origin of retention failure in ferroelectric memor ies (FeRAMs) with SrBi2(Ta; Nb)(2)O-9 (SBTN) memory cell capacitors by considering the time-dependent behavior of polarization vs. voltage ( P-V) curves of the capacitors during high-temperature storage. Since t he SBTN capacitors exhibited no marked decrease in the nonvolatile com ponent of polarization even after high-temperature storage, we focused on the effect of voltage shift observed in P-V curves. We calculated bitline voltage along the storage from the P-V curves and the bitline capacitance, and successfully estimated a decrease in the bitline volt age, which is in agreement with the retention failure in FeRAMs. In ad dition, the calculation indicated that the lifetime limited by the ret ention failure in FeRAMs with SBTN capacitors at 125 degrees C exceeds 10 years.