Reversible fatigue-rejuvenation procedure and its mechanism in Hf0.5Zr0.5O2epitaxial films

HfO₂-based ferroelectrics, such as Hf_0.5Zr_0.5O₂, arouse great attention in recent years because of their CMOS compatibility and robust nano-scale ferroelectricity. However, fatigue is one of the toughest problems for ferroelectric applications. The fatigue mechanism of HfO₂-based ferroelectrics is different from conventional ferroelectric materials, and research on the fatigue mechanism in HfO₂-based epitaxial films have been rarely reported. In this work, we fabricate 10 nm Hf_0.5Zr_0.5O₂epitaxial films and investigate the fatigue mechanism. The experimental data show that the remanent ferroelectric polarization value decreased by 50% after 10⁸cycles. It is worth noting that the fatigued Hf_0.5Zr_0.5O₂epitaxial films can be recovered through applying electric stimulus. Combined with the temperature-dependent endurance analysis, we propose that fatigue of our Hf_0.5Zr_0.5O₂films comes from both phase transition between ferroelectric Pca2₁and antiferroelectric Pbca as well as defects generation and dipole pinned. This result offers a fundamental understanding of HfO₂-based film system, and could provide an important guideline for subsequent studies and future applications.

Large-Scale Hf0.5 Zr0.5 O2 Membranes with Robust Ferroelectricity

Hafnia-based compounds have considerable potential for use in nanoelectronics due to their compatibility with complementary metal-oxide-semiconductor devices and robust ferroelectricity at nanoscale sizes. However, the unexpected ferroelectricity in this class of compounds often remains elusive due to the polymorphic nature of hafnia, as well as the lack of suitable methods for the characterization of the mixed/complex phases in hafnia thin films. Herein, the preparation of centimeter-scale, crack-free, freestanding Hf_0.5 Zr_0.5 O₂ (HZO) nanomembranes that are well suited for investigating the local crystallographic phases, orientations, and grain boundaries at both the microscopic and mesoscopic scales is reported. Atomic-level imaging of the plan-view crystallographic patterns shows that more than 80% of the grains are the ferroelectric orthorhombic phase, and that the mean equivalent diameter of these grains is about 12.1 nm, with values ranging from 4 to 50 nm. Moreover, the ferroelectric orthorhombic phase is stable in substrate-free HZO membranes, indicating that strain from the substrate is not responsible for maintaining the polar phase. It is also demonstrated that HZO capacitors prepared on flexible substrates are highly uniform, stable, and robust. These freestanding membranes provide a viable platform for the exploration of HZO polymorphic films with complex structures and pave the way to flexible nanoelectronics.