Ferroelectric Random Access Memories

TLDR

Ferroelectric random‑access memory (FeRAM) is a nonvolatile memory that stores data via hysteretic polarization–electric field characteristics; only capacitor‑type FeRAMs are commercially available, and advances in stacked ferroelectric capacitors and high‑remanent‑polarization materials are essential for high‑density memory fabrication. This review surveys the history and characteristics of FeRAMs. The authors analyze ferroelectric film properties—particularly Pb(Zr,Ti)O₃, SrBi₂Ta₂O₉, and BiFeO₃—and discuss capacitor‑type FeRAM cell structures and operation principles. Experimental results on an optimized gate structure in ferroelectric‑gate field‑effect transistors demonstrate excellent data‑retention performance.

Abstract

Ferroelectric random access memory (FeRAM) is a nonvolatile memory, in which data are stored using hysteretic P-E (polarization vs. electric field) characteristics in a ferroelectric film. In this review, history and characteristics of FeRAMs are first introduced. It is described that there are two types of FeRAMs, capacitor-type and FET-type, and that only the capacitor-type FeRAM is now commercially available. In chapter 2, properties of ferroelectric films are discussed from a viewpoint of FeRAM application, in which particular attention is paid to those of Pb(Zr,Ti)O3, SrBi2Ta2O9, and BiFeO3. Then, cell structures and operation principle of the capacitor-type FeRAMs are discussed in chapter 3. It is described that the stacked technology of ferroelectric capacitors and development of new materials with large remanent polarization are important for fabricating high-density memories. Finally, in chapter 4, the optimized gate structure in ferroelectric-gate field-effect transistors is discussed and experimental results showing excellent data retention characteristics are presented.