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

Abstract

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.

Keywords:

• FeRAM
• retention
• BLT
• sensing margin