Wafer-scale flexible 2D PtSe2 layers with bi-directional wavelength tunability for fully optical synaptic operations

Abstract

Artificial synapses are promising building blocks for neuromorphic computing, offering a pathway to overcome the fundamental limitations of the von Neumann architecture. Especially, synaptic devices operated with optical stimuli are gaining interest due to their distinct advantages over electrically modulated conventional memristors. Here, we report fully optical synaptic demonstrations in two-dimensional (2D) platinum diselenide (PtSe₂) layers, leveraging their bidirectional photo-responsiveness. Wafer-scale 2D PtSe₂ layers grown by chemical vapor deposition (CVD) exhibit distinct photoconductive responses: positive photoconductivity under long-wavelength optical illumination (625–940 nm) and negative photoconductivity under short-wavelength illumination (405 nm). This unique wavelength tunability leads to a comprehensive and essential set of optical synaptic characteristics in 2D PtSe₂ layers integrated on flexible substrates; i.e., wavelength-dependent excitatory post-synaptic current (EPSC) and inhibitory post-synaptic current (IPSC), paired-pulse facilitation (PPF), as well as transitions between short-term/long-term potentiation (STP/LTP) and short-term/long-term depression (STD/LTD). Such synaptic features are well preserved even in the 2D PtSe₂ layers-based devices undergoing severe mechanical deformation, which facilitates demonstrations of basic logic functions and Pavlovian associative learning. Furthermore, wafer-scale 2D PtSe₂ arrays on diverse substrates are demonstrated to yield optical pattern recognition, retention, and potentiation capabilities accompanying minimal device-to-device variations. These findings highlight new opportunities for fully-optical and mechanically-reconfigurable neuromorphic hardware with extreme thinness.