Designing wake-up free ferroelectric capacitors based on the $\mathrm{HfO_2/ZrO_2}$ superlattice structure

TL;DR

This paper introduces a unidirectional annealing technique for HfO2/ZrO2 superlattice ferroelectric capacitors that eliminates wake-up effects, enhances stability, and maintains high remanent polarization at moderate temperatures.

Contribution

The study proposes a novel unidirectional annealing method from the Pt/ZrO2 interface that suppresses wake-up phenomena in hafnia-based ferroelectric capacitors, improving device stability.

Findings

Unidirectional annealing at 600°C from Pt/ZrO2 interface yields wake-up free ferroelectric capacitors.

Heating from TiN/HfO2 side or at 500°C requires wake-up process, showing the importance of annealing direction.

Pt/ZrO2 configuration prevents high leakage current and memristor behavior, enhancing device reliability.

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 $\mathrm{Hf_{0.5}Zr_{0.5}O_2}$ (HZO) superlattice ferroelectrics, which involves heating from the $\mathrm{Pt/ZrO_2}$ interface side. Nanoscale $\mathrm{ZrO_2}$ 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 $\mathrm{600^oC}$ 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 $\mu\mathrm{C/cm^2}$. On the other hand, heating from the $\mathrm{TiN/HfO_2}$ side, or using $\mathrm{500^oC}$ annealing temperature, both yield ferroelectric devices that require a wake-up process. The special configuration of $\mathrm{Pt/ZrO_2}$ is verified by comparative studies with several other superlattice structures and HZO solid-state solutions. It is discovered that heating from the $\mathrm{Pt/HfO_2}$ side at $\mathrm{600^oC}$ 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.