Multilevel MoS₂ Optical Memory with Photoresponsive Top Floating Gates

Optoelectronic memory devices, whose states can be controlled using electrical optical signals, are receiving much attention for their potential applications in image sensing and parallel data transmission and processes. Here, we report MoS₂-based devices with top floating gates of Au, graphene, and MoS₂. Unlike conventional floating gate memory devices, our devices have the photoresponsive floating gate at the top, acting as a charge trapping layer. Stable and reliable switching with an on/off ratio of ∼10⁶ and a retention time of >10⁴ s is achieved by illumination with 405 nm light pulses as well as application of gate voltage pulses. However, upon illumination with 532 or 635 nm light pulses, multilevel optical memory effects are observed, which are dependent on the wavelength and the optical exposure dosage. In addition, compared to the device employing a graphene floating gate, the device with an MoS₂ floating gate is more sensitive to light, suggesting that the multilevel optical memory properties originate from photoexcited carriers in the top floating gate and can be modulated by adjusting the top floating gate materials. The structure of the top floating gate may open up a new way to novel optoelectronic memory devices.