Recent progress in ferroelectirc memory technology

Recent progress in ferroelectric random access memory (FeRAM) technology is reviewed from viewpoints of materials, devices, and circuits. First, insulating and ferroelectric properties of pure and Mn-substituted BiFeO
₃
thin films are discussed. It is shown that Mn substitution at the Fe site is effective in improving the breakdown characteristics of the films and obtaining saturated polarization vs electric field (P-E) hysteresis loops at room temperature. Then, memory characteristics of FET-type FeRAM are discussed. It is shown that on-and off-currents in a ferroelectric-gate FET can be retained over 30 days when a HfO
₂
buffer layer is inserted between the ferroelectric film and Si substrate in the gate structure. Finally, recent progress in another FET-type memory, 1T2C-type FeRAM, is introduced, in which the operation characteristics of 1k-bit memory array are mainly discussed