• • Improper ferroelectrics, where polarization is a secondary order parameter, exhibit intrinsic immunity to depolarization fields, enabling polarization stability in ultrathin films (e.g., below 5 nm) without the critical thickness limit observed in proper ferroelectrics like BaTiO3 and PbTiO3.
• • Hyper-ferroelectric materials, such as LiZnSb, retain polarization under strong depolarization fields due to their unique electronic structure, with theoretical predictions indicating polarization stability even at 2D limits, as supported by first-principles calculations.
• • HfO2-based quasi-2D ferroelectrics demonstrate thickness-independent polarization and depolarization-field immunity, making them promising for high-density memory integration with endurance exceeding 10^10 cycles and switching speeds below 10 ns.
• • 2D van der Waals ferroelectrics, including exfoliated Aurivillius oxide flakes of sub-unit cell thickness, exhibit robust in-plane ferroelectricity at room temperature, with polarization values up to 20 μC/cm², enabling scalable device fabrication without lattice mismatch constraints.