Mesoscopic-scale grain formation in HfO2-based ferroelectric thin films and its impact on electrical characteristics

• Published in: Nano convergence 2022-11, Vol.9 (1), p.50-50, Article 50
• Main Authors: Kobayashi, Masaharu, Wu, Jixuan, Sawabe, Yoshiki, Takuya, Saraya, Hiramoto, Toshiro
• Format: Article
• Language: English
• Subjects: Chemistry and Materials Science; Electric fields; Ferroelectric HfO2; Ferroelectric materials; Ferroelectricity; Fluorite Structure Ferroelectric Materials and Devices; Grain boundaries; Hafnium oxide; Kinetics; Linear polarization; Materials Science; Memory devices; Nanoscale Science and Technology; Nanotechnology; Nanotechnology and Microengineering; Nonuniformity; Orientation; Switching; Thermodynamics; Thickness; Thin films
• ISSN: 2196-5404; 2196-5404
• DOI: 10.1186/s40580-022-00342-6

Ferroelectric memory devices are expected for low-power and high-speed memory applications. HfO 2 -based ferroelectric is attracting attention for its CMOS-compatibility and high scalability. Mesoscopic-scale grains, of which size is almost comparable to device size, are formed in HfO 2 -based ferroelectric poly-crystalline thin films, which largely influences electrical characteristics in memory devices. It is important to study the impact of mesoscopic-scale grain formation on the electrical characteristics. In this work, first, we have studied the thickness dependence of the polarization switching kinetics in HfO 2 -based ferroelectric. While static low-frequency polarization is comparable for different thickness, dynamic polarization switching speed is slower in thin Hf 0.5 Zr 0.5 O 2 (HZO) capacitors. Based on the analysis using the NLS model and physical characterization, thinner HZO contains smaller grains with orientation non-uniformity and more grain boundaries than thicker HZO, which can impede macroscopic polarization switching. We have also theoretically and experimentally studied the polar-axis alignment of a HfO 2 -based ferroelectric thin film. While in-plane polar orientation is stable in as-grown HZO, out-of-plane polarization can be dominant by applying electric field, which indicates the transition from in-plane polar to out-of-plane polar orientation in the ferroelectric phase grains. This is confirmed by calculating kinetic pathway using ab-initio calculation.