Multistate\nFerroelectric Diodes with High Electroresistance\nBased on van der Waals Heterostructures

Some van der Waals\n(vdW) materials exhibit ferroelectricity,\nmaking\nthem promising for novel nonvolatile memories (NVMs) such as ferroelectric\ndiodes (FeDs). CuInP<sub>2</sub>S<sub>6</sub> (CIPS) is a well-known\nvdW ferroelectric that has been integrated with graphene for memory\ndevices. Here we demonstrate FeDs with self-rectifying, hysteretic\ncurrent–voltage characteristics based on vertical heterostructures\nof 10 nm thick CIPS and graphene. By using vdW indium–cobalt\ntop electrodes and graphene bottom electrodes, we achieve a high electroresistance\n(on- and off-state resistance ratios) of ∼10<sup>6</sup>, an\non-state rectification ratio of 2500 for read/write voltages of 2\nV/0.5 V, and a maximum output current density of 100 A/cm<sup>2</sup>. These metrics compare favorably with state-of-the-art FeDs. Piezoresponse\nforce microscopy measurements show that stabilization of intermediate\nnet polarization states in CIPS leads to stable multibit data retention\nat room temperature. The combination of two-terminal design, multibit\nmemory, and low-power operation in CIPS-based FeDs is potentially\ninteresting for compute-in-memory and neuromorphic computing applications.