Study Of 2D Material Memristors And Its Neuroplasticity In Brain

Compared to supercomputers,the human brain has superior computing performance due to its higher signal processing speed and lower power consumption in high integration densities.In the neural network of the human brain,synapses are the smallest gaps in which signals are transmitted between neurons and play the role of simulating logic,memory and learning.Memristors as artificial synapses can replicate the basic function of biological synapses and mimic the way the brain works.However,the traditional oxide memristor has fallen into a bottleneck that cannot be improved in terms of power consumption and storage performance.Thus,the research and development of memristor devices based on new materials has become extremely important.In response to the above problems,this study found that a class of five-atom MXenes（Ti₃C₂）has been reported for the fabrication of memristor with bipolar switching behavior.However,other triatomic and heptadic materials are rarely used as the resistive switching layer of memristors.In our work,triatomic MXene（V₂C）was taken as an example to compare its electronic properties and structural stability with pentatom MXene（Ti₃C₂）by theoretical calculation.And two kinds of Ag/V₂C/W and Ag/Ti₃C₂ were fabricated.The electrical characteristics of the memristor were tested and compared.At the same time,a series of research and analysis on the synaptic plasticity of brain nerves have been carried out to provide underlying support for the exploration of the interconnection of neuromorphic devices and the brain-like integration architecture.This thesis mainly completes the following work:1.MXene materials were fully investigated,and their electrical properties and structural stability were explored through first-principles calculations based on density functional theory,including energy bands,density of states（local density of states and projected density of states）and Phonon spectrum.At the same time,the diffusion coefficient and electrical conductivity of silver ions in V₂C MXene were calculated to be higher than those of Ti₃C₂ material.In addition,V₂C and Ti₃C₂nanosheets were prepared by V₂Al C and Ti₃Al C₂,respectively,and their physical characterizations were analyzed by SEM and XRD.And the MXene resistive switching layer was prepared by spin coating method,which was introduced into the memristor.2.In our work,the Ag/V₂C/W and Ag/Ti₃C₂/W structures were fabricated,and a number of electrical tests were carried out to compare the differences in their characteristics to explore the influence of the introduction of triatomic and pentatom MXenes on the device performance.In this work,we found that the devices of both structure can exhibit resistive switching characteristics,and the resistive state also has good retention ability.But devices based on triatomic MXene V₂C show better stability and uniformity.At the same time,its on-off ratio is about 1000 times higher than that of the Ag/Ti₃C₂/W device.And the dispersion of high/low resistance states in the cycle test is also lower than that of the Ag/Ti₃C₂/W device.This work shows that triatomic V₂C can also become the resistive switching layer of memristors,and at the same time,it may be due to the high diffusion coefficient and high electrical conductivity of silver ions in V₂C,resulting in strong conduction in Ag/V₂C/W devices.filaments,which also makes the device better than the Ag/Ti₃C₂/W device in terms of stability and uniformity.3.Since the Ag/V₂C/W memristor exhibits excellent repeatability and stable retention,this work further studies its synaptic bionics in neural networks,such as continuous conductance regulation behavior,short-term plasticity simulation and spike timing-dependent plasticity.The research results show that the device can successfully simulate the function of human brain synapses by regulating the synaptic weights,showing that the device has excellent potential for application in neural networks.