Device Physics of Ferroelectric Thin-Film Memories

Abstract

Band structure match-ups are given theoretically from X-ray photoemission spectroscopy (XPS) for the electrode interfaces between platinum electrodes and the ferroelectric thin-film materials commonly used for random access memories (DRAMs and nonvolatile FRAMs): strontium bismuth tantalate (SBT), barium strontium titanate (BST), and lead zirconate titanate (PZT). The results all agree with experimentally measured Schottky barrier heights. The electronegativity constant or S-factor (derivative of Schottky barrier height with respect to electron affinity) is found to be approximately 0.7 for these materials, not the purely ionic value of 1.0. The reduction of a factor of a million in the effective Richardson coefficient is explained. And the paradox of avalanche breakdown but decreasing breakdown fields with increasing temperature is reconciled.