Two-Dimensional MXene Synapse for Brain-Inspired Neuromorphic Computing.

MXenes, an emerging class of two-dimensional (2D) transition metal carbides and nitrides, have attracted wide attention because of their fascinating properties required in functional electronics. Here, an atomic-switch-type artificial synapse fabricated on Ti3 C2 Tx MXene nanosheets with lots of surface functional groups, which successfully mimics the dynamics of biological synapses, is reported. Through in-depth analysis by X-ray photoelectron spectroscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy, it is found that the synaptic dynamics originated from the gradual formation and annihilation of the conductive metallic filaments on the MXene surface with distributed functional groups. Subsequently, via training and inference tasks using a convolutional neural network for the Canadian-Institute-For-Advanced-Research-10 dataset, the applicability of the artificial MXene synapse to hardware neural networks is demonstrated.

Negative differential transconductance device with a stepped gate dielectric for multi-valued logic circuits.

Multi-valued logic (MVL) technology is a promising approach for improving the data-handling capabilities and decreasing the power consumption of integrated circuits. This is especially attractive as conventional complementary metal-oxide-semiconductor technology is approaching its scaling and power density limits. Here, an ambipolar WSe2 field-effect transistor with two or more negative-differential-transconductance (NDT) regions in its transfer characteristic (NDTFET) is proposed for MVL applications of various radices. The operation and charge carrier transport mechanism of the NDTFET are studied first by Kelvin probe force microscopy, electrical, and capacitance-voltage measurements. Next, strategies for increasing the number of NDT regions and engineering the NDTFET transfer characteristic are discussed. Finally, the extensibility and tunability of our concept are demonstrated by adapting NDTFETs as core devices for ternary, quaternary, and quinary MVL inverters through simulations, where only WSe2 is employed as a channel material for all devices comprising the inverters. The MVL inverter operation principle and the mechanism of the multiple logic state formation are analyzed in detail. The proposed concept is practically verified by the fabrication of a ternary inverter.

A multiple negative differential resistance heterojunction device and its circuit application to ternary static random access memory.

For increasing the restricted bit-density in the conventional binary logic system, extensive research efforts have been directed toward implementing single devices with a two threshold voltage (VTH) characteristic via the single negative differential resistance (NDR) phenomenon. In particular, recent advances in forming van der Waals (vdW) heterostructures with two-dimensional crystals have opened up new possibilities for realizing such NDR-based tunneling devices. However, it has been challenging to exhibit three VTH through the multiple-NDR (m-NDR) phenomenon in a single device even by using vdW heterostructures. Here, we show the m-NDR device formed on a BP/(ReS2 + HfS2) type-III double-heterostructure. This m-NDR device is then integrated with a vdW transistor to demonstrate a ternary vdW latch circuit capable of storing three logic states. Finally, the ternary latch is extended toward ternary SRAM, and its high-speed write and read operations are theoretically verified.