| Non-volatile random resistance memory is most promising to become the next generation novel information memory due to its superior performance such as fast resistance switching speed,easy construction,low energy consumption.The recording and reading of information in memristor are realized based on the characteristics of switching between high resistance state and low resistance state under external excitation.According to previous reports,oxygen vacancy migration is one of the most important reasons for resistance switching.However,the mechanism of oxygen vacancy remains controversial.The mechanisms of vacancy migration,vacancy formation of conductive wires and vacancy capture of electrons are still interlaced,and the excitation conditions are not clear,which delays the development of memristors dominated by oxygen vacancy.Traditional memristors based on thin film have strong crystal surface scattering,which masks the mechanism of oxygen vacancies.Therefore,a one-dimensional resistive memory based on hexagonal tungsten trioxide?h-WO3?nanowires is constructed,and the mechanism of vacancy-dominated resistance transition is explored by changing the oxygen vacancy concentration.The specific research results are as follows:1.Controllable preparation of h-WO3 nanowires was realized by hydrothermal method.The diameter and length of nanowires can be effectively controlled by changing temperature by adjusting the reaction temperature,reaction time,stoichiometric ratio of reactants and types of inducers.The h-WO3 nanowires were synthesized with diameters typically in the range of 70-500 nm and a,lengths up to15?m and with a small number of vacancies.2.The concentration of oxygen vacancy in nanowires can be controlled by regulating the temperature and time of oxidized and reduced.When the reduced temperature rises from room to 673K and keep the time for 40 minutes,the nanowires maintain good morphology and high crystallinity,meanwhile the concentration of oxygen vacancies?1.38%-14.27%?is effectively regulated.The experimental results show that the removing/generation of oxygen vacancies occurs mainly in the radial/axial direction of nanowires during oxidized/reduced process.With the increasing of vacancy concentration,the lattice disorder enhances,and the defect level gradually moves up and overlaps with the bottom of the conduction band to inducing the Anderson localization.3.By analyzing the I-V characteristic curves,the mechanism of resistance switching controlled by oxygen vacancies is further clarified.Under low oxygen vacancy concentration,the resistance state switch from low to high resistance and the memristor exhibit bipola.The fitted results of I-V curves show that the conduction mechanism is dominated by SCLC mechanism.However,under high oxygen vacancy concentration,the memristor turns on at high resistance state,showing unipolar characteristics,and the overall conductivity decreases significantly.The conductive mechanism of memristor no longer conforms to SCLC mechanism.This is attributed to the strong lattice disorder caused by defects,which induces Anderson localization,inhibiting carrier migration and shields the emission of localized electrons.Applied the high bias scanning or continuous repetitive negative pulses,the oxygen vacancies migrates directional reducing the lattice disorder,resulting in the degeneration of Anderson localized,and then the memristor display bipolarity characteristic again.The conduction mechanism dominant by SCLC controlled by traps energy levels.And I-V curves display the NDC phenomenon.Experiments show that the polarity of memristor can be changed by changing the oxygen vacancies concentration,which is beneficial to the construction of multi-stage memory.At the same time,the mechanism of oxygen vacancy capture and oxygen vacancy transition can be induced by large bias or repetitive pulse stimulation,which promotes the understanding of oxygen defect resistance mechanism and facilitates the development of memristor. |
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