Enhanced Ferroelectric Properties and Insulator-Metal Transition-Induced Shift of Polarization-Voltage Hysteresis Loop in VO-Capped HfZrO Thin Films.

A capping layer is known to be critical for stabilizing the ferroelectric (FE) orthorhombic phase (o-phase) in a HfO-based thin film. Here, vanadium oxide (VO), a functional oxide exhibiting the insulator-metal transition, is used as a novel type of a capping layer for the HfZrO (HZO) thin film. It is demonstrated that the VO capping layer (VCL) can enhance the FE properties of the HZO thin film comprehensively. Specifically, the HZO thin film with a VCL shows large remanent polarization (2 ≈36.9 μC/cm), relatively small coercive field ( ≈1.09 MV/cm), high endurance (up to 10 cycles), and long retention (>10 seconds). The enhanced FE properties may be attributed to the VCL-induced stabilization of the FE o-phase and suppression of oxygen vacancies at the interface. Furthermore, the HZO thin film with a VCL exhibits a successive rightward shift of polarization-voltage () hysteresis loop as the temperature increases. This is well correlated with the insulator-metal transition in a VCL, which can modulate the interfacial built-in field and thus cause the loop shift. It is therefore demonstrated that a VCL not only enhances the FE properties of HZO thin films but also provides a temperature degree of freedom to modulate the FE properties, which may open up a new pathway to develop HfO-based FE memories with high performance and novel functionalities.