Two-Terminal Multibit Optical Memory via van der Waals Heterostructure

2D van der Waals (vdWs) heterostructures exhibit intriguing optoelectronic properties in photodetectors, solar cells, and light-emitting diodes. In addition, these materials have the potential to be further extended to optical memories with promising broadband applications for image sensing, logic gates, and synaptic devices for neuromorphic computing. In particular, high programming voltage, high off-power consumption, and circuital complexity in integration are primary concerns in the development of three-terminal optical memory devices. This study describes a multilevel nonvolatile optical memory device with a two-terminal floating-gate field-effect transistor with a MoS₂ /hexagonal boron nitride/graphene heterostructure. The device exhibits an extremely low off-current of ≈10^-14 A and high optical switching on/off current ratio of over ≈10⁶ , allowing 18 distinct current levels corresponding to more than four-bit information storage. Furthermore, it demonstrates an extended endurance of over ≈10⁴ program-erase cycles and a long retention time exceeding 3.6 × 10⁴ s with a low programming voltage of -10 V. This device paves the way for miniaturization and high-density integration of future optical memories with vdWs heterostructures.