Atomic layer deposition of HZO ferroelectric films beyond the upper thickness limit via tetragonal-phase nucleation engineering

Atomic-layer-deposited hafnium zirconium oxide (HZO) ferroelectric films have emerged as highly promising candidates for next-generation ferroelectric devices. However, the stabilization of the ferroelectric phase in HZO films thicker than 20 nm remains a persistent challenge, fundamentally limiting their applications in piezoelectric transducers, pyroelectric detectors, and energy storage devices. Here, we propose a tetragonal-phase nucleation strategy guided by phase-field simulation, breaking through the thickness barrier for high-performance ferroelectric HZO films. Through a newly developed phase-field crystallization model, we first identify that a higher initial density of tetragonal-phase nuclei concurrently enhances low-temperature crystallinity and promotes the formation of the ferroelectric orthorhombic phase. Furthermore, an innovative HZO (3.5 nm)/ZrO2 (2.5 nm) multilayer film is designed to increase tetragonal-phase nucleation density. The 54-nm-thick film annealed at an unprecedentedly low temperature of 400 °C exhibits a high fraction of ferroelectric phase and excellent ferroelectric properties. Notably, it achieves a remanent polarization significantly exceeding that of sub-20-nm-thick HZO films prepared by conventional processes. Our study advances the understanding of ferroelectric phase formation in HZO films while simultaneously extending their technological applicability.