Electronic synaptic devices are important building blocks for neuromorphic computational systems that could go beyond the constraints of von Neumann architecture. Although two-terminal memristive devices have been demonstrated to be possible candidates, they suffer from several shortcoming related to the filament formation mechanism including non-linear switching, write noise, and high device conductance, all of which limit the accuracy and energy efficiency. Electrochemical three-terminal transistors, in which the channel conductance can be tuned without filament formation provide an alternative platform for synaptic electronics. Here, we demonstrate an all-solid-state electrochemical transistor made with Li-ion-based solid dielectric and two-dimensional α-phase molybdenum oxide (α-MoO 3 ) nanosheets as the channel. These devices achieve nonvolatile conductance modulation in an ultralow conductance regime (<75 nS) by reversible intercalation of Li-ions into the α-MoO 3 lattice. Based on this operating mechanism, the essential functionalities of synapses, such as short-and longterm synaptic plasticity and bidirectional near-linear analog weight update have been demonstrated. Simulations using the handwritten digits data sets demonstrate high recognition accuracy (94.1%) of the synaptic transistor arrays. These results provide an insight into the application of two-dimensional oxides for large-scale, energy-efficient neuromorphic computing networks.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Biological synapses store and process information simultaneously by tuning the connection between two neighboring neurons. Such functionality inspires the task of hardware implementation of neuromorphic computing systems. Ionic/electronic hybrid three-terminal memristive devices, in which the channel conductance can be modulated according to the history of applied voltage and current, provide a more promising way of emulating synapses by a substantial reduction in complexity and energy consumption. 2D van der Waals materials with single or few layers of crystal unit cells have been a widespread innovation in three-terminal electronic devices. However, less attention has been paid to 2D transition-metal oxides, which have good stability and technique compatibility. Here, nanoscale three-terminal memristive transistors based on quasi-2D α-phase molybdenum oxide (α-MoO ) to emulate biological synapses are presented. The essential synaptic behaviors, such as excitatory postsynaptic current, depression and potentiation of synaptic weight, and paired-pulse facilitation, as well as the transition of short-term plasticity to long-term potentiation, are demonstrated in the three-terminal devices. These results provide an insight into the potential application of 2D transition-metal oxides for synaptic devices with high scaling ability, low energy consumption, and high processing efficiency.

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