Ferroelectricity of Hf0.5Zr0.5O₂ Thin Films Free From the Influence of Electrodes by Using Al₂O₃ Capping Layers

Ferroelectricity of Hf _0.5 Zr _0.5 O ₂ thin films prepared by plasma-enhanced atomic layer deposition (PEALD) with and without TiN electrodes was demonstrated. Excellent ferroelectricity of Hf _0.5 Zr _0.5 O ₂ thin films was confirmed by both polarization versus voltage ( ${P}$ ,– ${V}$ ) and piezoresponse force microscopy (PFM) hysteresis loops. The $2{P}_{r}$ value can reach as high as $53 ~\mu \text{C}$ /cm ² under a sweep voltage of 8 V with TiN top and bottom electrodes. By introducing Al ₂ O ₃ capping layer (AOCL), the $2{P}_{r}$ value of the sample can reach $47 \mu \text{C}$ /cm ² that is less sensitive to the annealing temperatures and electrode materials. At the same time, the leakage current is also significantly reduced. The typical ${P}$ ,– ${V}$ loops can always be observed for samples with different electrode materials or annealing temperatures. These results are beneficial to practical applications in nonvolatile memories and synaptic devices.