Effects of oxygen vacancies on ferroelectric characteristics of RF-sputtered Hf0.5Zr0.5O2

Abstract

Ferroelectric memories composed of all-sputtered films were fabricated, and the ferroelectric properties of the sputtered Hf0.5Zr0.5O2 (HZO) were analyzed by modulating the amount and location of oxygen vacancies (OVs), which were controlled by changing the type of ambient gas (N2 and O2) during annealing. Based on the analysis of the oxygen vacancy (OV) distribution in HZO, it was found that the OV in HZO could be diminished through O2 annealing, and the leakage current could be suppressed by the reduced OV. In particular, it is more sensitively reduced with a decreasing amount of OV (OV_near) near where electron injection occurs for trap-assisted tunneling (TAT). Thus, the memory window and on-off ratio of the ferroelectric tunneling junction (FTJ) memory were improved owing to the reduced TAT with decreasing OV_near. Furthermore, it was observed that undesirable depolarization, which degraded the retention characteristics, initiated at approximately 0 V. Through the different depolarization phenomena, which depended on the annealing conditions, it was confirmed that the polarization reversal at approximately ±0 V was caused by the OV_near-induced depolarization field.