Improved Ferroelectricity in Cryogenic Phase Transition of Hf0.5Zr0.5O2

Cryogenic transition from metastable tetragonal phase (t-phase) to orthorhombic phase (o-phase) is crucial in achieving the desired ferroelectric characteristics. Observing the reversible transition from anti-ferroelectricity (AFE) to ferroelectricity (FE) in electrical characteristics, the cryogenic phase transition is experimentally analyzed in Hf0.5Zr0.5O2 alloys. Furthermore, the stabilized o-phase formation is more favorable when applying cryogenics to superlattice Hf0.5Zr0.5O2, manifesting a 23% increase in remanent polarization (Pr) at 77K. To theoretically clarify the emergence of phase transition with decreasing temperatures, Landau–Ginzburg–Devonshire theory and first-principle study are combined in this work. Based on the detailed calculation, the increasing relative free energy of the t-phase contributes to lowering the energy barrier when decreasing the temperature, making the convenient transitional pathway from metastable t- to o-phase. This work exhibits the cryogenic phase transition model involving t- and o-phases in Hf0.5Zr0.5O2 and presents a method to boost ferroelectricity for emerging HfO2-based cryo-device.