Epitaxial Hf_0.5Zr_0.5O₂ films: A temperature dependence study

Hafnia-based films are gaining prominence in the advancement of next-generation memory and logic devices. Their significance arises from their pronounced ferroelectricity at the nanoscale and their synergy with silicon processes. However, there are questions surrounding how their polarization stability responds to changes in temperature. In our study, we synthesized (111)-oriented Hf_0.5Zr_0.5O₂ (HZO) ferroelectric thin films through pulsed laser deposition. This process corroborated the domain-matching epitaxy growth mechanism. We observed that HZO films possess distinct temperature-dependent ferroelectric traits. Specifically, a decrease in temperature triggers a fall in remanent polarization. Notably, the coercive field diminishes initially, only to rebound around the 200 K mark. Utilizing low-temperature in situ x-ray diffraction techniques, we have identified that lattice strain, induced by the differing thermal expansion of the films due to temperature changes, alters the migration rate of oxygen vacancies, resulting in the observed variations in remanent polarization and coercive field as reported in the article. Our findings deepen the understanding of ferroelectric mechanisms inherent in hafnia-based oxide thin films.