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 MoS 2 -based devices with top floating gates of Au, graphene, and MoS 2 . 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 ∼10 6 and a retention time of >10 4 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 MoS 2 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.

We fabricated MoS-based flash memory devices by stacking MoS and hexagonal boron nitride (hBN) layers on an hBN/Au substrate and demonstrated that these devices can emulate various biological synaptic functions, including potentiation and depression processes, spike-rate-dependent plasticity, and spike-timing dependent plasticity. In particular, compared to a flash memory device prepared on an hBN substrate, the device fabricated on the hBN/Au exhibited considerably more symmetric and linear bidirectional gradual conductance change curves, which may be attributed to the device structure incorporating double floating gate. For the device on the hBN/Au, electron transfers may occur between the floating gate MoS and Au, as well as between the floating gate MoS and the channel MoS, allowing for more control over electron tunneling and injection. To test our hypothesis, we also fabricated a MoS-based flash memory device on an hBN/Pd substrate and found behavior similar to the device fabricated on hBN/Au. Our results demonstrate that flexible synaptic electronics may be implemented using MoS-based flash memory devices with double floating gates.

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Three type of modular networks are constructed using polydimethylsiloxane (PDMS) microstructures fabricated on a multi-electrode array (MEA) without transfer to investigate how neuronal activities are affected by modular network structure.