Ferroelectric hafnium dioxide, particularly in its doped forms such as Si-doped or Y-doped HfO₂, has emerged as a promising candidate for non-volatile memory applications due to its compatibility with CMOS processes and robust ferroelectric properties at nanoscale dimensions. With a bandgap of approximately 5.7 eV, HfO₂-based ferroelectrics offer advantages in terms of scalability and integration, especially for embedded DRAM and emerging memory technologies. The ferroelectric phase in HfO₂ is metastable and can be stabilized through doping, strain engineering, or careful control of deposition conditions. This article explores the mechanisms behind ferroelectricity in doped HfO₂, its wake-up effects, endurance limitations, and integration with GaN power transistors, while contrasting its properties with traditional perovskite ferroelectrics.

The ferroelectric behavior in HfO₂ arises from the non-centrosymmetric orthorhombic phase (Pca2₁), which is induced by doping elements such as silicon or yttrium. These dopants introduce oxygen vacancies and lattice distortions that stabilize the ferroelectric phase. The wake-up effect, a critical phenomenon in HfO₂-based ferroelectrics, refers to the gradual increase in remanent polarization during initial cycling. This effect is attributed to the redistribution of oxygen vacancies and the reorientation of domains. Studies indicate that wake-up typically occurs within the first 10⁴ to 10⁵ cycles, after which the polarization stabilizes. However, excessive cycling leads to fatigue, where the ferroelectric performance degrades due to defect accumulation and phase instability. Endurance limitations in HfO₂ ferroelectrics are generally observed beyond 10¹⁰ cycles, though this varies with doping concentration and interface quality.

Integration of ferroelectric HfO₂ with GaN power transistors presents unique opportunities for next-generation power electronics. GaN transistors benefit from the high breakdown field and electron mobility of GaN, while HfO₂ ferroelectrics provide non-volatile memory functionality without requiring additional materials or complex processing steps. The combination enables monolithic integration of memory and power devices, reducing parasitic effects and improving system efficiency. Key challenges include managing the thermal budget during fabrication, as GaN devices typically require high-temperature processing, which may affect the ferroelectric properties of HfO₂. Additionally, interface states between HfO₂ and GaN must be minimized to ensure reliable switching and retention.

Compared to perovskite ferroelectrics like Pb(Zr,Ti)O₃ (PZT), HfO₂ offers several scalability advantages. PZT suffers from severe degradation at thicknesses below 100 nm due to interfacial dead layers and leakage currents. In contrast, HfO₂ maintains ferroelectricity even at sub-10 nm thicknesses, making it suitable for advanced nodes in semiconductor manufacturing. Furthermore, HfO₂ is compatible with existing CMOS processes, eliminating the need for exotic materials or deposition techniques. The absence of lead in HfO₂ also addresses environmental and regulatory concerns associated with PZT. However, perovskite ferroelectrics still exhibit superior polarization values (20-50 µC/cm² for PZT vs. 10-30 µC/cm² for doped HfO₂) and lower coercive fields, which may be critical for certain applications.

For embedded DRAM applications, doped HfO₂ provides a compelling alternative to conventional capacitors. Its high dielectric constant and ferroelectric switching enable higher density and lower power operation compared to traditional SiO₂ or high-k dielectrics. The scalability of HfO₂ allows for continued miniaturization, addressing the limitations of perovskite-based ferroelectrics in sub-20 nm technologies. Additionally, the compatibility with silicon substrates simplifies integration into existing fabrication flows, reducing cost and complexity.

Wake-up effects and endurance remain key challenges for HfO₂ ferroelectrics. The wake-up process, while beneficial for stabilizing polarization, introduces variability in device performance during initial operation. Strategies to mitigate this include pre-cycling devices before deployment or optimizing doping profiles to minimize oxygen vacancy mobility. Endurance can be improved through defect engineering, such as incorporating nitrogen to passivate vacancies or using layered structures to distribute stress during cycling. Recent studies have demonstrated endurance exceeding 10¹² cycles in optimized Y-doped HfO₂ films, though further work is needed to achieve comparable performance across all device geometries.

In conclusion, ferroelectric HfO₂ represents a transformative material for non-volatile memory and power electronics integration. Its compatibility with CMOS processes, scalability, and environmental advantages over perovskites position it as a leading candidate for future memory technologies. While challenges such as wake-up effects and endurance persist, ongoing research in doping, interface engineering, and device integration continues to advance the performance and reliability of HfO₂-based ferroelectrics. The synergy between HfO₂ and GaN further expands its potential, enabling novel applications in power-efficient and high-performance electronic systems. As the semiconductor industry pushes toward smaller nodes and more complex integration, doped HfO₂ stands out as a versatile and scalable solution for embedded memory and beyond.