Research On Resistive Switching Mechanism Of Binary Oxide Films

As the traditional flash memory is meeting its physical limits,the resistance random access memory（RRAM）has attracted much attention because of its potential application for the next generation nonvolatile memory.However,the mechanism of RRAM is still unknown,which baffled its application greatly.In our works,we have fabricated the NiO and Al₂O₃ based RRAM by using radio frequency magnetron sputtering method.The mechanisms of unipolar and bipolar resistive switching,as well as the sneak path problem,have been studied.By using first-principles calculation method,the characters of filaments consisting of oxygen vacancies（V_O）have been studied.The coexistence of bipolar and unipolar resistive switching has been realized in Pt-Ir/NiO/TiB.The type of switching is controlled by polarity of set voltage(V_set),and is free from the influence of compliance current.The types of filaments show polarity dependence of V_set,and the magnitude of negative V_set is less than that of positive one.These results come from the mechanism of breakdown and its influence on formation of filaments.Coexistence of bipolar and unipolar resistive switching accompanied with self-rectifying effect in has been realized in Pt-Ir/NiO/n-Si system.We find the self-rectifying effect in Pt-Ir/NiO/n-Si comes from the schottky contact between filaments and n-Si.Based on coexistence of bipolar and unipolar resistive switching（RS）in one Pt-Ir/Al₂O₃/TiB memory switching cell,the difference in V_set and its influences on RS behaviors between the two switching types are studied.The results show that the RS types are dominated by magnitude and polarities of V_set.The bipolar RS can only be induced by the negative V_set with small magnitude.There are two types of polarity dependence of V_set exist in insulator,which come form the difference in mechanism of breakdown.The resistances of low resistance state（LRS）decrease with the increasing of V_set in unipolar RS while the resistances of LRS in bipolar RS show complex dependence on V_set.It reveals that the V_O-filaments properties and RS types are controlled by the breakdown mechanisms and polarities of V_set.The dispersity of V_set in Al₂O₃ based RRAM can be reduced by inserting NiO layer,which can be explained by RCB model.The properties of V_O-filaments in NiO and MgO have been studied by using first-principles calculation method.The results show that the cohesion energy of V_O-filaments is a function of charge states of V_O.The V_O chain presents semiconductor properties in MgO.The V_O chain presents takes metal properties in NiO.The results match the experiment results well.