Origin of Temperature‐Dependent Ferroelectricity in Si‐Doped HfO2

The structural origin of the temperature‐dependent ferroelectricity in Si‐doped HfO2 thin films is systematically examined. From temperature‐dependent polarization‐electric field measurements, it is shown that remanent polarization increases with decreasing temperature. Concurrently, grazing incidence X‐ray diffraction shows an increase in the orthorhombic phase fraction with decreasing temperature. The temperature‐dependent evolution of structural and ferroelectric properties is believed to be highly promising for the electrocaloric cooling application. Magnetization measurements do not provide any indication for a change of magnetization within the temperature range for the strong crystalline phase transition, suggesting that magnetic and structural properties are comparatively decoupled. The results are believed to provide the first direct proof of the strongly coupled evolution of structural and electrical properties with varying temperature in fluorite oxide ferroelectrics. The structural origin of the temperature‐dependent ferroelectricity in Si‐doped HfO2 film is elucidated using in situ X‐ray diffraction and electrical characterization with varying temperature. The nonferroelectric tetragonal to ferroelectric orthorhombic phase transition can be confirmed both from changes in structure and electrical properties. The giant electrocaloric effect in Si‐doped HfO2 film is attributed to the temperature‐induced phase transition.