Metastable phases and memory applications of ferroelectric HfO₂: materials insights and system-level perspectives

Ferroelectric hafnium oxide (HfO₂) has gained major interest for its strong polarization, excellent endurance, and CMOS compatibility, making it ideal for next-generation microelectronic devices. This review critically examines the structural phases of HfO₂, focusing on the metastable orthorhombic Pca2₁ phase responsible for ferroelectricity. Mechanisms such as doping, strain, interfacial effects, and oxygen vacancy engineering that stabilize this phase are analyzed, along with the influence of processing parameters like ALD, annealing, and film thickness on device behavior. Advanced characterization and DFT simulations elucidate polarization and defect interactions. The integration of HfO₂ into memory and logic architectures demonstrates its promise for scalable non-volatile memory, energy-efficient computing, and neuromorphic hardware. At the circuit and system level, the review connects ferroelectric phase and defect physics to variability-aware design of FeFET/FTJ arrays, in-/near-memory accelerators, and HfO₂-based sensors, showing how coercive-field dispersion and endurance-retention trade-offs affect BER and efficiency.