Fatigue and switching in ferroelectric memories: Theory and experiment

TLDR

Earlier theories of switching are extended to include finite grain sizes, surface nucleation, triangular drive pulses, and dipolar forces. The study presents a theoretical model of fatigue in ferroelectric thin‑film memories based on impact ionization leading to dendritic growth of oxygen‑deficient filaments. The model predicts spontaneous polarization versus switching cycles, compared with Monte Carlo simulations of a two‑dimensional Ising model and experimental data from small‑grain sol‑gel PZT films. The model shows excellent agreement with experiment, reproducing the linear relationship between switching time and polarization during fatigue and matching sol‑gel PZT switching data.

Abstract

A theoretical model of fatigue in ferroelectric thin-film memories based upon impact ionization (e.g., Ti+4 to Ti+3 conversion in PbZr1−xTixO3), resulting in dendritic growth of oxygen-deficient filaments, is presented. The predictions of spontaneous polarization versus switching cycles Ps(N) are compared with both Monte Carlo simulations for a two-dimensional Ising model and with experimental data on small-grain (40 nm) sol-gel PZT films. Excellent agreement between theory and experiment is obtained. In addition to modeling the Ps(N) curves, the theory developed explains the observed linear proportionality between switching time ts(N) and polarization Ps(N) during fatigue; other models of aging do not account for this. Earlier theories of switching are also extended to include finite grain sizes, surface nucleation, triangular drive pulses, and dipolar forces. Good agreement with sol-gel PZT switching data is obtained.