| The new generation of nonvolatile memory mainly include ferroelectric random access memory,phase change random access memory,magnetic random access memory and resistance random access memory（RRAM）.Among them,RRAM based on resistance switching（RS）has the advantages of high storage density,low power consumption,fast access speed,long working life,and low cost,which has attracted widespread attention from researchers from all walks of life.We have found resistance switching in a variety of oxide materials,but there are still differences in RS mechanisms.In addition,different relaxation phenomena have been observed.The time relaxation of the resistance state will cause the loss of stored data and the instability of logic operations.At present,there are only few papers focused on the source of resistive relaxation.These have become obstacles in RRAM storage applications.Therefore,it is necessary to study the resistive performance and stability performance of the device to optimize the storage performance of RRAM.NiO and Nb:SrTiO3（NSTO）materials are representative RS materials.In this thesis,based on these two materials,devices with NiO/NSTO,NiO/Pt and Pt/NSTO structures have been prepared.Through detailed research on its RS performance and resistance state retention performance,the physical origin of the resistance-state relaxation phenomenon of non-volatile resistive switching devices is revealed.The details are as follows:1.Explore the resistance relaxation feature of nonvolatile memory based on NiO material.NiO thin film grown on Pt and 0.7 wt%NSTO（100）single crystal substrate by pulsed laser deposition technology.Pt/NiO/Pt and Pt/NiO/NSTO/In devices show filament-type and interface-type RS behaviors,respectively.The unipolar and bipolar RS effect mechanisms are dominated by the filament type and the interface type respectively.The resistance retention test shows that these two different RS types exhibit distinct resistance evolutions.For filament-type Pt/NiO/Pt device,both high and low resistance states have stable retention performance,and no obvious relaxation phenomenon is found around 2000 s,demonstrating that the conducting filament is stable once it is formed.For interface-type Pt/NiO/NSTO/In device,the multi-level resistance states obtained by changing the magnitude of the negative and positive write voltages,respectively show a relaxation phenomenon of decreasing and increasing trends.Interestingly,we can clearly see from the relaxation phenomenon:the relaxation trends of multilevel resistance states depend on the polarity of write voltage;the multi-level resistance state will become stable after relaxation,and the stabilized resistance state is not changed until write voltage is large enough.Synthesize the test results and use fitting analysis to get:the resistance relaxation phenomenon is due to charge migration,the nonvolatility of resistance is due to the interface state electrons trapping/detrapping.2.Explore the influence of different Nb doping concentration on the resistance relaxation feature of Pt/NSTO/In devices.The above work shows that the resistance nonvolatility and resistance relaxation of the interface type RS are caused by the interface state electrons trapping/detrapping and charge migration,respectively.Studies have shown that different concentrations of Nb doping will affect the interface state density and barrier height.In this work,we selected 0.05 wt%and 0.7 wt%NSTO single crystals as the research object to control the interface state density and barrier height,and explore them influence on the resistance relaxation performance.The research on the electrical properties of Pt/0.7 wt%NSTO/In and Pt/0.05 wt%NSTO/In devices show that:the resistance switching phenomenon is caused by the change of the interface barrier height;During the initial holding time,the multi-level resistance states show a relaxation phenomenon of decreasing and increasing trends respectively;However,as the holding time increases,the multi-level resistance state of the Pt/0.7 wt%NSTO/In device tends to be stable,and the multi-level resistance state of the Pt/0.05 wt%NSTO/In device shows an upward trend of relaxation.C-V test shows that the interface state density of Pt/0.7 wt%NSTO and Pt/0.05 wt%NSTO are 3.48×1013 e V-1cm-2 and 2.11×1013e V-1cm-2,respectively;Schottky fitting shows Pt/0.7 wt%the interface barrier heights of NSTO and Pt/0.05wt%NSTO are 0.72 e V and 0.66 e V in the high resistance state,respectively,and 0.53 e V and 0.48 e V in the low resistance state,respectively.In summary,we draw the following conclusions:during the initial holding time,the opposite resistance state relaxation direction is caused by charge migration;as the holding time increases,the resistance state of the Pt/0.7 wt%NSTO/In device tends to be stable It shows that a large interface state density and barrier height are beneficial to the stability of the resistance state. |
