Polarization-controlled memristive synapse characteristics of HfZrO₂-based ferroelectric switchable diode

To realize artificial synapse functionalities using precisely controllable resistance-switching characteristics in electronic synaptic devices, we demonstrated diverse and efficient synaptic functions on a two-terminal device architecture of the Au/HfZrO₂/Pt ferroelectric switchable diode. The ferroelectric properties of the HfZrO₂ active layer were enhanced by forming a crystallographic orthorhombic phase, which was associated with an increased oxygen vacancy density. The fabricated device exhibited distinct asymmetric hysteresis behavior, attributed to the switchable diode effect resulting from ferroelectric polarization-induced modulation of the Schottky barrier height. This polarization-mediated barrier modulation enabled systematic tuning of the on-state current values by varying the sweep time duration. These finely tunable resistive-switching characteristics allowed the fabricated device to effectively emulate biological synaptic functions. Controlled time intervals and pulse durations in repetitive pulse schemes provided a straightforward method to improve both the linearity and symmetry of long-term memory characteristics, thereby enhancing learning accuracy and training efficiency. Furthermore, this approach facilitated metaplasticity in spike-timing-dependent plasticity, corresponding to the learning activity of the electronic synapse. These findings underscore the significant potential of the Au/HfZrO₂/Pt ferroelectric switchable diode for applications in neuromorphic computing systems.