Study On The Performance And Mechanism Of Ion-doped Resistive Random Access Memory Based On Polyelectrolyte

With the rise of artificial intelligence,the amount of data globally has increased dramatically,memristor-based neuromorphic computing has realized the integration of computing and storage,which is expected to break the limitations of von Neumann’s traditional computer architecture.Therefore,it is necessary to develop synaptic devices with memory and computing functions.However,memristor-based synapses still face many challenges,such as poor conductance potentiation/depression linearity and large differences from biological synapses.Simultaneously,flexible electronics are also advancing rapidly,the flexibility of Resistive Random Access Memory（RRAM）is essential as a candidate for next-generation memory.Therefore,in terms of both closeness to biological properties and flexibility,organic materials are chosen as the dielectric layer for this thesis.Generally,organic materials are used as redox materials or ionic pathway materials for dielectric layer.The latter is more suitable for application in artificial synapses than the former,as the diffusion of metal ions can better mimic the diffusion of Ca²⁺in biological synapses.However,the organic materials currently used contain both positive and negative ions,and their effect on ion diffusion is unclear.Therefore,in this thesis,PEI and PAA,polyelectrolytes with a single charge in the functional groups,are chosen as the dielectric layer materials for the study of the performance optimisation of polyelectrolyte-based RRAM and simulation of artificial synapses.In this thesis,memories using positive-charged polyethyleneimine（PEI）and negative-charged polyacrylic acid（PAA）as dielectric are prepared.First,the effect of polyelectrolyte charge type on the performance of ITO/PEI-Ca²⁺/ITO and ITO/PAA-Ca²⁺/ITO devices is investigated.The results show that only ITO/PAA-Ca²⁺/ITO exhibits stable and uniform bipolar resistive switching（RS）behavior,indicating that the charge type of the polyelectrolyte is a decisive factor to achieve RS in the Ca²⁺doped devices.The process conditions of ITO/PAA-Ca²⁺/ITO are then optimised in terms of four aspects:spin-coating speed,polyelectrolyte solution concentration,ion doping concentration and dielectric layer thickness.The results show that the device performance is achieved optimally at the solution concentration of 0.25wt%,the doping concentration of c（-COOH）:c(Ca²⁺)=1:1,the thickness of the dielectric layer of 20nm,the spin coating speed of 3000 rpm and the time of 30s.Finally,the ITO/PAA-Ca²⁺/ITO device also simulates complete synaptic functions such as short-term and long-term plasticity,paired-pulse facilitation and spike-timing-dependent plasticity.The innovative ITO/PAA-Ca²⁺/ITO device is proposed:using a simple ion doping process to improve the performance of the device,while confirming that the formation of Ca²⁺flux is restricted by the same charge type in the organic dielectric layer and facilitated by the opposite charge matrix in the organic dielectric layer.It provides valuable practice for the application of organic materials in memristor,as well as synapse emulation.