Designing wake-up free ferroelectric capacitors based on the $\mathrm{Hf}{\mathrm{O}}_2/Zr{\mathrm{O}}_2$ superlattice structure

Abstract

The wake-up phenomenon widely exists in hafnia-based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at higher temperatures have been reported to be effective in eliminating wake-up, but high temperature may yield the monoclinic phase or generate high concentration oxygen vacancies. In this work, a unidirectional annealing method is proposed for the crystallization of $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ (HZO) superlattice ferroelectrics, which involves heating from the $Pt/Zr{\mathrm{O}}_2$ interface side. Nanoscale $\mathrm{Zr}{\mathrm{O}}_2$ is selected to resist the formation of monoclinic phase, and the chemically inert Pt electrode can avoid the continuous generation of oxygen vacancies during annealing. It is demonstrated that $600^{\mathrm{o}}\mathrm{C}$ annealing only leads to a moderate content of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake-up free nature and a $2P_{\mathrm{r}}$ value of 27.4 $\hat{I}¼C/c{\mathrm{m}}^2$. On the other hand, heating from the $TiN/Hf{\mathrm{O}}_2$ side, or using $500^{\mathrm{o}}\mathrm{C}$ annealing temperature, both yield ferroelectric devices that require a wake-up process. The special configuration of $Pt/Zr{\mathrm{O}}_2$ is verified by comparative studies with several other superlattice structures and HZO solid-state solutions. It is discovered that heating from the $Pt/Hf{\mathrm{O}}_2$ side at $600^{\mathrm{o}}\mathrm{C}$ leads to high leakage current and a memristor behavior. The mechanisms of ferroelectric phase stabilization and memristor formation have been discussed. The unidirectional heating method can also be useful for other hafnia-based ferroelectric devices.

16 pages, 7 figures