Non-centrosymmetric crystallization in ferroelectric hafnium zirconium oxide via photon-assisted defect modulation

Abstract

Ferroelectricity in Hf_1-xZr_xO₂ (HZO) thin films has garnered significant attention for advanced memory devices. However, the challenge in understanding nanoscale polymorphism and the absence of non-centrosymmetric crystallization techniques compatible with back-end-of-line processes have restricted its broader application to various types of information storage systems. In this study, we report a novel method to generate the ferroelectric orthorhombic phase (o-phase) in HZO films via photon-assisted non-centrosymmetric crystallization. As-prepared HZO films (8 nm) prepare by atomic layer deposition underwent thermal annealing and subsequent deep ultraviolet (DUV) irradiation. The DUV treatment successfully triggered ferroelectricity in HZO films annealed at 300 °C. Moreover, the same post-treatment applied to HZO films annealed at 400 °C led to a further enhanced polarization up to 29.2 μC cm⁻² under high bipolar triangular pulses and outstanding reliability for up to 10⁶ bias stress cycles. Finally, based on in-depth microscopic and structural analyses, we proposed the mechanism on the symmetry-breaking phase transformation to the o-phase HZO with advanced ferroelectricity via oxygen vacancy-driven lattice rearrangement.