Ultrahigh remanent polarization of Ce-doped HfO2 ferroelectric thin films through strain engineering
Hafnium oxide (HfO2)-based ferroelectrics are compatible with complementary metal-oxide-semiconductor (CMOS) processing and lead-free, but their remanent polarization (2Pr) remains insufficient for advanced non-volatile memory. This work achieves an ultrahigh 2Pr of 102.1 μC/cm2 in Ce-doped HfO2 thin films via biaxial strain engineering. Hf0.85Ce0.15O2−δ films were grown on crystallographically oriented SrTiO3 (STO) substrates, and the substrate orientation was found to control Ce3+ content, unit cell volume, and ferroelectric phase stabilization. Films on (011)-oriented STO exhibit the highest Ce3+ fraction and largest unit cell volume, corresponding to chemical negative strain that stabilizes the metastable orthorhombic phase. The optimized films show 2Pr = 102.1 μC/cm2, the highest reported for HfO2-based ferroelectrics, and fatigue resistance with <10% degradation after 107 switching cycles. Piezoresponse force microscopy confirms robust polarization switching with ~180° phase reversal under ±10 V bipolar cycling. The results establish substrate-induced strain as a viable route to overcome the polarization bottleneck of HfO2-based materials, providing a foundation for high-density, low-power non-volatile memory and in-memory computing.