Impact of Hf_0.5Zr_0.5O₂ ferroelectric film thickness on the wake-up effect and endurance of memory cells

This work presents a comprehensive study of the correlation between the structural/ferroelectric properties of Hf_0.5Zr_0.5O₂ (HZO) thin films – the functional layers for ferroelectric non-volatile memory – and their thickness in the 5–10 nm range. X-ray diffraction analysis revealed the predominant presence of the polar orthorhombic Pca _{2 1} phase in all samples. The highest content of (002)-oriented domains, corresponding to the vertical orientation of the polar axis, was found in the 8 nm thick films. Electrical measurements demonstrated an inverse relationship between film thickness and the breakdown field, which varied from 6.5 MV/cm (5 nm) to 4.5 MV/cm (10 nm). A pronounced improvement in switching endurance was observed with decreasing thickness: films of 5–6 nm maintained stable ferroelectric characteristics up to 10⁹–10¹⁰ switching cycles at an electric field of 3.0 MV/cm. Analysis of the I–V characteristic dynamics during wake-up with bipolar pulses showed that the parameter stabilization process is accompanied by a merging of the switching current peaks and an increase in the remanent polarization up to 30 μC/cm². It was established that degradation in thin films begins significantly later (after >10⁶ cycles) than in thick ones (10⁴–10⁵ cycles). This is presumably associated with the inhibitory effect of the amorphous phase on the kinetics of diffusion and drift of charged defects. The obtained results are valuable for the development of reliable ferroelectric memory devices, demonstrating an optimal combination of high remanent polarization and cycling stability in ultra-thin HZO films.

ferroelectric non-volatile memory, ferroelectric hafnium oxide, switching endurance, wake-up process, electric breakdown