Physical Mechanisms behind the Field‐Cycling Behavior of HfO₂‐Based Ferroelectric Capacitors

TLDR

HfO₂-based ferroelectrics offer full scalability and CMOS integrability, unlike perovskite FeRAMs, yet the mechanisms underlying their wake‑up and fatigue regimes remain unknown. This study aims to identify the root cause of the remnant‑polarization increase during wake‑up and its subsequent degradation with cycling. Through ferroelectric switching current measurements, Preisach density analysis, TEM, TCAD modeling, and trap‑density spectroscopy, the authors show that wake‑up involves redistribution—not creation—of existing defects, while vacancy diffusion drives phase transformation. The main finding is that vacancy diffusion is the key mechanism behind the phase transformation and the observed increase in remnant polarization during wake‑up.

Abstract

Novel hafnium oxide (HfO 2 )‐based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite‐based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake‐up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake‐up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake‐up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.