Layered Perovskites with Giant Spontaneous Polarizations for Nonvolatile Memories

Abstract

A series of titanate-based layered perovskites having large values of the spontaneous polarization $P_s$ were developed for their applcations to nonvolatile ferroelectric random access memories. Among these, the Nd-modified bismuth titanate [${\mathrm{B}\mathrm{i}}_{4-x}{\mathrm{N}\mathrm{d}}_x{\mathrm{T}\mathrm{i}}_3{\mathrm{O}}_{12}$ (BNdT)] system exhibited the most remarkable ferroelectric properties. The $c$-axis oriented BNdT capacitor was characterized by a switchable remanent polarization $2P_r$ of over $100\mu \mathrm{C}/{\mathrm{c}\mathrm{m}}^2$ and imprinting and fatigue-free behavior. The active Ti site responsible for the giant $P_s$ was identified with the help of Rietveld analysis, x-ray absorption near-edge structure study, and ab initio quantum computations.