Abstract
Two-dimensional (2D) van der Waals (vdW) materials have recently attracted considerable attention due to their excellent electrical and mechanical properties. TmPSx (where Tm = a transition metal), which is a new class of 2D vdW materials, is expected to show various physical phenomena depending on the Tm used. In this paper, the unprecedented synaptic behavior of a vertical Ag/CrPS4/Au capacitor structure, where CrPS4 is a single-crystalline 2D vdW layer, is reported. Multi-stable resistive states were obtained using an external voltage of less than 0.3 V. Both short-term plasticity and long-term potentiation were observed by controlling the interval of the external voltage pulse. Simple mechanical exfoliation was used to develop a synaptic device based on a very thin CrPS4 layer with a thickness of ~17 nm. Therefore, it was demonstrated that vertical Ag/CrPS4/Au capacitors could be promising inorganic synaptic devices compatible with next-generation, flexible neuromorphic technologies.
Highlights
Conductive-bridge random access memory (CBRAM), which exploits electrochemically active ion migration, has been proposed as a potential candidate for future nonvolatile memory applications[1,2,3]
short-term plasticity (STP) is achieved through the temporal enhancement of a synaptic connection, while repeated stimulation causes a permanent change in the connection, leading to LTP12–16
The crystallinity and chemical composition of the CrPS4 crystals were confirmed through Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) analyses, respectively
Summary
Conductive-bridge random access memory (CBRAM), which exploits electrochemically active ion migration, has been proposed as a potential candidate for future nonvolatile memory applications[1,2,3]. In metal oxide and chalcogenide electrolyte materials that display both ionic and electronic conductivity, ion migration is associated with reduction and oxidation processes. These processes result in large electrical conductance changes, characteristic of ion-controlled memristors, with the application of an external bias[3,4,5]. Learning, forgetting, and memorization events in the human brain can be described using the modulation of the synaptic weights between pre-neurons and post-neurons. This phenomenon is known as synaptic plasticity. 1015 synapses consume only ~10 W per synaptic event with a duration of ~100 ms, and a low energy consumption and an extremely small size are required for a synaptic memristor device to be applied in a neuromorphic system[9,10]
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