Artificial synapse based on MoO<sub>3</sub> nanosheets prepared by hydrothermal synthesis

Abstract

<sec>Recently, neuromorphic systems capable of parallel information processing have attracted increasing attention. A neuromorphic system is desired to emulate a human brain, which consists of hundreds of billions of neurons connected with even more synapses. Synapses are important connection parts between neurons to transmit information through release and reception of neurotransmitters. A neuromorphic system could replicate brain learning, cognition and computation of a human brain to process huge data with 10<sup>16</sup> floating point numbers per second. The high computing efficiency has attracted many researchers to study artificial synapses for application in future artificial intelligence. The synaptic weight could be adjusted by the received information. This provides a basis for the learning and computing capability of artificial synapses. </sec><sec>So far, a number of semiconductor materials have been used in artificial synaptic devices, like some organic materials, e.g. Poly(3-hexylthiophene-2,5-diyl)(P3HT), [1]Benzothieno[3,2-b][1]benzothiophene, 2,7-dioctyl-(C8-BTBT) etc, some inorganic oxides such as zinc oxide, indium zinc oxide(IZO), indium gallium zinc oxide(IGZO), transition metal oxides, etc, and two-dimensional materials, e.g. graphene, black phosphorus, and organic-inorganic hybrid perovskite materials. Among them, transition metal oxides are attractive due to their unique layered structure and inherent properties, which are important in photohydrolysis, lithium ion batteries, and field-effect transistors. MoO<sub>3</sub>, as a typical transition-metal oxide, has been used in artificial synaptic devices, with different preparation methods, such as mechanical exfoliation, chemical vapor deposition (CVD) and chemical vapor transportation (CVT), pulse-laser deposition (PLD). Here, we report the preparation of a semiconductor layer of MoO<sub>3</sub> nanosheets by hydrothermal method, and the use of a TiO<sub>2</sub> nanoparticle seed layer to improve the adhesion of MoO<sub>3</sub> nanosheets. This is a cost-effective and controllable process. The high surface-to-volume ratio of the material provides large contact area at the interface to allow easy ion diffusion. The device emulates important synaptic functions, such as excitatory post-synaptic current (EPSC), paired-pulse facilitation (PPF), spike-duration dependent plasticity (SDDP), spike-voltage dependent plasticity (SVDP) and spike-rate dependent plasticity (SRDP). This work could be an important addition to the neuromorphic research field.</sec>