Scale-up and optimization of HfO2-ZrO2 solid solution thin films for the electrostatic supercapacitors

Highlights: • The field-induced ferroelectricity was acquired from the Hf_0.5Zr_0.5O₂ thin film. • Chemical/structural changes by the decreased deposition temperature were elucidated. • The crystallization in the as-deposited state was minimized by controlling Zr content and T_dep. • The electrostatic HfO₂-ZrO₂ capacitor were scaled-up for the large energy storage. • The FFE Hf_0.5Zr_0.5O₂ capacitor does not degrade even after 10¹⁰ switching cycles and up to 175 °C. To date, the high energy storage performances observed in the field-induced ferroelectric HfO₂- or ZrO₂-based films have had an obstacle to scale-up due to the involvement of low-k monoclinic phase at the large thickness (> ~ 10 nm). Considering that the monoclinic phase formation is closely related with the in-situ (partial) crystallization during the atomic layer deposition (ALD) process, in this work, the ALD temperature of Hf_0.5Zr_0.5O₂ thin films was lowered, and its influence on the energy storage performances was systematically examined. Carbon and nitrogen dopants incorporated at a low deposition temperature in combination with grain size decrease change the polymorphism of Hf_0.5Zr_0.5O₂ thin film from the genuine ferroelectric to field-induced (incipient) ferroelectric crystal structure. The Hf_0.5Zr_0.5O₂ thin film deposited at 210 °C shows improved resistance to degradation by monoclinic phase involvement up to ~ 40 nm compared to the previously-reported Hf_0.3Zr_0.7O₂ thin films. By investigating Hf_0.5Zr_0.5O₂ thin films with wide ALD temperature and thickness ranges, energy storage density of ~ 55 J cm⁻³ with an efficiency of ~ 57% can be achieved at the ~ 7.1 nm Hf_0.5Zr_0.5O₂ thin films deposited at 215 °C. The performance can be retained even after 10¹⁰ bipolar switching cycles, and the film endures thermal stress up to 175 °C without severe degradation, demonstrating notable reliability.