Modulation of oxygen vacancy filaments and crystal structure by thermal annealing for high-performance solution-processed HfZrOx resistive memory

Abstract

This study demonstrates solution-processed Ti/HZO/n⁺-Si write-once-read-many-times (WORM) memory devices. By systematically evaluating HZO resistive switching (RS) layers annealed from 300 °C to 900 °C, we establish a direct correlation between temperature-dependent evolution of oxygen vacancies, structural crystallinity, and the resulting RS performance.XPS and XRD analyses reveal that increasing the temperature facilitates a structural transition of the HZO films from an amorphous state to a polycrystalline monoclinic phase, while reducing the oxygen vacancy concentration from 43.9% to 17.3%. Temperature-dependent measurements combined with different voltage sweep directions confirm that the RS mechanism of the memories is governed by oxygen-vacancy conductive filaments. The 700 °C-annealed device exhibits optimal performance, featuring an ultralow OFF-state current of ~10^-11 A, a remarkable ON/OFF current ratio of ~10⁷ , and high-speed switching of ~30 ns with a low programming energy of ~114.4 pJ, while maintaining robust data retention and read-disturb immunity extrapolated to safely exceed 10 years at an elevated temperature of 85 °C. This filamentary process is degraded at lower temperatures by excessive leakage paths and is completely suppressed at 900 °C due to severe vacancy reduction and the formation of a highly insulating monoclinic HfO2 phase.