Huge On/Off Current Ratio of a LiNbO₃ Domain-Wall Memory with Asymmetric Electrode Geometries

High-density nonvolatile memories seek for crossbar architecture with the number of in-series cells limited by ON/OFF current ratios of selectors. Here we found one strategy to increase the ratio up to 10⁸; for a ferroelectric LiNbO₃ domain-wall memory, where ON/OFF currents originate from the creation/elimination of a conducting domain wall between two antiparallel/parallel domains controlled by bipolar write voltages applied to two side Cu electrodes. The two electrodes were fabricated in different depths (166 nm vs. 235 nm) into the LiNbO₃ film thickness. The asymmetric electrode geometries promote the formation of more conductive head-to-head domains after suppressing tail-to-tail domain growth. The tailored memory devices demonstrate robust endurance over 10⁹ switching cycles and good retention in time exceeding 10⁶; s and can be operated in nanosecond speeds with an activation field lowered by 2-3 times.