Strain Modulation of ZrO2 Ferroelectric Thin Films for Achieving Superior Polarization
Zirconia (ZrO2)-based fluorite ferroelectric materials are promising for nonvolatile memory and logic devices due to their CMOS compatibility and cost advantages over hafnium oxide (HfO2). However, the metastable nature of the ferroelectric orthorhombic phase (o-phase) hinders practical application. Here, we report the strain-mediated stabilization of the ferroelectric o-phase in ZrO2 thin films grown on niobium-doped strontium titanate (NSTO) substrates with different crystallographic orientations via chemical solution deposition. Systematic structural and ferroelectric characterization, combined with simulation, reveals that substrate orientation controls in-plane tensile strain, selectively promoting epitaxial growth of the o-phase. The ZrO2 film on NSTO(110) exhibits the highest o-phase content, achieving a remanent polarization (2Pr) of 92.64 μC/cm², which remains as high as 88.54 μC/cm² after resistive-capacitive (RC) delay calibration. The device shows endurance of approximately 10^7 cycles with favorable fatigue characteristics. X-ray absorption spectroscopy (XAS) further indicates distortion of Zr-O tetrahedra, providing microscopic insight into the ferroelectricity. This work presents a novel strategy for property tuning of ZrO2 films and supports their application in storage and logic devices.