Research On The Electrical Performance Characteristics And Mechanism Of Embedded Nanoislands On Hafnium Oxide Multilayer Composite Memristors

One of the memristor applications is in the constructed crossbar array implementing the vector matrix addition and multiplication,it could realize the in-memory computing,which might solve the urgent need for high data processing speed and low energy consumption requirement in the era of big data.However,the crossbar array constructed by the memristors has the problem of leakage current.With the help of the threshold switching behavior of the diffusive memristors,it is expected to reduce the impact of leakage current.However,the need for electroforming process,poor tolerance and unstable device performance are the key factors that limit the application of diffusive memristors.In order to investigate the factors affecting the performance and their stability of diffusive memristors from the point of view of material composition and structure,the following research work was conducted and the instructuive results were concluded:（1）We have prepared the Au/Ag/Hf O_x/Hf O₂/Ag-NI（Nano Island）/Au devices.The different stoichiometric ratios of hafnium oxides were obtained by atomic layer deposition and plasma enhanced atomic layer deposition,respectively,and the embedded Ag nanoislands were prepared using AAO as a hard mask combined with electron beam evaporation deposition.Electrical performance test results showed that the use of Ag nanoislands eliminated the need for an electroforming process for the devices and greatly reduced the variation of the device threshold voltages.Compared with Au/Ag/Hf O_x/Hf O₂/Ag/Au devices,the coefficient of variation of V_th^- and V_th⁺ of Au/Ag/Hf O_x/Hf O₂/Ag-NI/Au devices was reduced by 43.26%and 30.1%,respectively.In addition,the devices containing embedded Ag nano-islands showed better tolerance.（2）In order to limit the amount of metal ions in the dielectric layer,Hf O_x:Ag layers were prepared by co-deposition,instead of the previous use of Ag layers and Ag nano-islands as Ag sources,and as the blocking layer,Ti O₂ barrier layers of different thicknesses were prepared by magnetron sputtering.We investigated the effect of Ti nano-islands and the thickness of the blocking layer on the selector devices.Electrical performance tests showed that Ti nano islands could reduce or even remove the Forming voltage of the selector,reduce the threshold switching voltage as well as the scattering of the threshold voltage,and reduce the leakage current;a certain thickness of the blocking layer could improve the tolerance of the devices,improve the switching ratio and the resistances of the high and low resistances of the devices,but a too thick layer could cause the device to require a Forming voltage,to shift from bipolar to unipolar to have a high leakage current,the too thick layer could reduce the tolerance of the devices,the switching ratio and the high and low resistances of the devices,and the threshold behaviors of the devices were slowed down or even the devices failed to undergo a threshold switching.（3）We tried to prepare Pt/Ta₂O₅/Hf O₂/Ti-NI/Ti N non-volatile devices in order to realize their usage in 1S1R structures,the Ta₂O₅ and Hf O₂ layers were prepared by using atom layer deposition,and the embdedded Ti nanoislands were prepared using AAO as a hard mask combined with electron beam evaporation deposition.Pt/Ta₂O₅/Hf O₂/Ti N devices without nanoislands were also prepared as comparison.The results showed that the introduction of Ti nano-islands increased the oxygen vacancies inside the Ta₂O₅/Hf O₂ layer,which increased the switching ratio of the Pt/Ta₂O₅/Hf O₂/Ti-NI/Ti N devices and has an obvious RESET process,but the SET voltage of the device as well as the high and low resistance variations increased,compared with Pt/Ta₂O₅/Hf O₂/Ti N devices.This paper provides processing parameters and systematic experimental results for diffusive memristors embedded with metal nano-island structures.The embedded nano-island structures can beneficially influence the electrical performances of the diffusive memristors such as could reduce or even remove the Forming voltage and reduce the threshold switching voltage as well as the scattering of the threshold voltage,which further improves the potential application of diffusive memristors in the field of crossbar arrays for in-memory computing.