Thermally Tunable Analog Memristive Behaviors in Sulfurized In2Se3 Nanoflakes for Bio-Plausible Synaptic Devices

Combining the intrinsic superiorities of two-dimensional materials and the emerging demand for neuromorphic computing, two-dimensional memristors have achieved huge advances in materials exploration and synaptic functionality emulation. However, their neuromorphic applications are still in the early stage since digital memristive behaviors for most of them are inconsistent with gradual biological synaptic plasticity. Here, we developed a simple approach to realize analog and thermal tunable memristive behaviors by introducing sulfur vacancies in CVD-grown In2Se3 nanoflakes through secondary sulfurization treatment. The density functional theory and ab initio molecular dynamics simulations confirm that sulfurized and defective In2Se3 can remain thermal stability at elevated temperatures up to 550 K. Therefore, we systematically investigated the temperature-dependent analog and tunable memristive behaviors and realized linear weight update with ultrawide dynamic range in sulfurized In2Se3 at high temperatures. The developed memristive device successfully emulates bio-realistic synaptic functionalities including transformation from short- to long-term plasticity, paired-pulse facilitation, posttetanic potentiation, spike-amplitude-dependent plasticity, spike-rate-dependent plasticity, and spike-time-dependent plasticity effects. It is unveiled that the formation energy of sulfur vacancy is greatly smaller than that of selenium, while their roughly same migration barriers can be modulated by electric field and temperature. Therefore, we put forward that the applied electric field can mediate vacancy migration in the sulfurized In2Se3 to gradually regulate the conductance, thereby realizing the emulation of synaptic plasticity. This work provides a promising approach to designing bio-plausible memristive devices for robust neuromorphic applications at high temperatures.