Dr. Xueliang Lyu successfully defended his PhD thesis, titled "Epitaxial Hf1-xZrxO2 Thin Films: Phase Stability, Polarization Enhancement, and Intrinsic Ferroelectric Response", on Wednesday, September 23, 2026. The research focuses on hafnium oxide-based ferroelectric materials, which are promising candidates for low-power, non-volatile memories compatible with existing silicon technology.
The thesis explores the growth of extremely thin crystalline films of hafnium–zirconium oxide, only a few nanometers thick. Lyu studied the growth conditions that favor the ferroelectric response and how to ensure that measurements truly correspond to intrinsic ferroelectricity and not extrinsic effects.
Key contributions include demonstrating that the ferroelectric phase is decided during high-temperature growth and is structurally robust. The influence of substrate orientation, growth atmosphere, and film thickness was also studied, finding that interface symmetry and oxygen chemistry are key to polarization, which reaches values above 30 μC/cm².
Furthermore, the research analyzed the full Hf1-xZrxO2 composition range, identifying that anomalously high polarization values in Zr-rich films stem from extrinsic effects, such as resistive switching, rather than genuine ferroelectricity. This establishes criteria for reliable evaluation.
This research is important for the development of low-power, non-volatile memories, crucial given the energy demands of artificial intelligence. The findings provide practical guidelines for engineering better materials and devices, and help ensure the reliability of results in the field.
Dr. Lyu joined ICMAB due to its expertise in growing high-quality epitaxial ferroelectric films. After his PhD, he will continue his research career as a postdoctoral researcher in China, focusing on ferroelectric materials and memory devices.
