Memristor Based On Carbon Dots/PVP Composite Film And Study On Resistance Characteristics

Memristor is considered to be the most promising hardware device for building resistance random access memory(RRAM)and neurosynaptic bionic devices,because of its unique nonlinear electrical characteristics.In recent years,memristors based on organic compound-doped quantum dot composite films have attracted much attention due to their excellent resistance and flexibility.As a new type of carbon nanomaterials,carbon quantum dots(CQDs)have excellent properties such as small size,stability,low production cost,and environmental protection.They have attracted much attention in electronic devices,fluorescent probes,and biomarkers.As an organic polymer,polyvinylpyrrolidone(PVP)has excellent water solubility,film-forming properties and ductility,and has become a research hotspot in flexible electronic devices in recent years.In this paper,CQDs were doped into PVP to form a CQDs-PVP composite film,and the charge trapping effect of CQDs surface defect sites is used to achieve stable resistance switching(RS)characteristics.By adjusting the voltage sweep range,a digital memristor with discrete changes in resistance and an analog memristor with continuous changes were realized in the same memristive system.The specific research content is as follows:1.Through the one-step hydrothermal method,conventional carbon quantum dots(UCQDs)and nitrogen-doped carbon quantum dots(NCQDs)with good dispersion and uniform size were obtained.By comparing Al/PVP/ITO,Al/UCQDs-PVP/ITO and Al/NCQDs-PVP/ITO devices,we found that:PVP devices without quantum dots do not have stable resistance change characteristics,and NCQDs doped PVP devices have better stability than UCQDs doped PVP devices.For NCQDs-doped PVP devices,we further adjusted the mass fraction of NCQDs doped.The research results show that devices with lower mass fractions(10%,20%,30%)have digital resistance change characteristics,while higher mass fractions(40%,50%,60%)of the devices have analog resistance change characteristics.2.Al/NCQDs-PVP/ITO devices with digital resistance change characteristics have excellent cycle endurance and retention characteristics.The operating voltage(V_SET/V_RESET)and resistance state(LRS/HRS)statistics show that the device has good working stability.Analysis shows that the resistive performance parameters of the device depend on the NCQDs doping mass fraction:with the increase of the doped NCQDs mass fraction,the stability of the device increases and the switching speed increases.Through double logarithmic fitting and theoretical analysis of the typical I-V curve of the device,it is concluded that the mechanism model of the resistive random access memory is a Space-Charge-Limited-Current(SCLC)mechanism based on charge trapping.3.For Al/NCQDs-PVP/ITO devices with analog resistive switching characteristics,we have realized the simulation of a variety of synaptic functions,including excitatory postsynaptic current(EPSC),short-term plasticity(STP),long-term plasticity(LTP),BCM learning rules.In addition,devices based on organic polymer materials have good flexibility and bending resistance.Finally,using the theoretical analysis of curve fitting and in-situ Kelvin probe force microscopy,the reasons for the difference in resistance characteristics caused by the mass fraction were analyzed,and the physical mechanism is discussed:the digital resistance characteristics depend on a main conductive path(CP),and the analog resistance change characteristic is attributed to the formation of multiple CPs.The conductance of the device can be continuously adjusted by controlling the number of multiple CPs.