Retention Characteristics of (Bi, La)4Ti3O12-Based FeRAMs

We have investigated the retention characteristics of ferroelectric random access memories (FeRAMs) using a bismuth layered perovskite, (Bi, La)4Ti3O12 (BLT). Due to the charge retention loss in ferroelectric storage capacitors, the sensing signal margin in FeRAM devices decreases from 920 mV at the retention time of 0.01 s to 770 mV at 100 s. From the logarithmic time dependence of the loss of obtained cell signals, the average margin of 520 mV is expected to remain after 10 y at 90°C. In addition, the slower retention loss rate in ferroelectric capacitors in long time retention region, suggests the high device reliability against retention degradation.