Phase modulation of Hf_0.5Zr_0.5O₂/La_0.7Sr_0.3MnO₃ heterostructure by growth orientation mediated strain engineering

Robust ferroelectric properties in HfO₂ based ultrathin films have the potential to revolutionize nonvolatile memories applications in nanoscale devices. However, to fully exploit the potential of ferroelectric HfO₂-based thin films, we must address fundamental questions regarding the origin of ferroelectricity and develop strategies for controlled implementation. The stability of the polar orthorhombic phase responsible for the robust polarization is believed to be influenced by various extrinsic factors, including finite-size effects, surface/interface effects of small grains, compressive stress, dopants, and oxygen vacancies. In this study, we investigate the influence of substrate orientations on the relative stability of different phases of Hf_0.5Zr_0.5O₂ (HZO) grown epitaxially on (001) and (110) oriented La_0.7Sr_0.3MnO₃ /SrTiO₃ using pulsed laser epitaxy (PLE). We demonstrate that stable polarization can be achieved in (111) oriented HZO in both types of the substrates however (110) oriented substrates promote a high degree of structural order (crystallinity) and better stability of the orthorhombic phase of HZO. Ferroelectric measurement reveals remanent polarization as high as 28 µC/cm² without any wake-up effect. This study suggests that tuning of the epitaxial growth of ferroelectric HZO with suitable strain conditions allows the improvement of stability of the metastable ferroelectric phase that could be used for better optimization of the device applications.