The Influence Of Nano-Islands On Resistance Switching Characteristics And Mechanism Of Hafnium Oxide Based Memristor Devices

The development of artificial intelligence and big data have increasingly high requirements for the performance of electronic information materials.Traditional electronic components have encountered bottlenecks in data storage,artificial neuron,simulation of synaptic and neuromorphic computing,while memristors are expected to build a new computing architecture system.The hafnium oxide is one of the most studied materials for memristors,and its application to non-volatile memristors have the property of adjustable conductivity,while its application to volatile memristors have the characteristic of threshold switching.The current threshold switching devices based on diffusive memristors still suffer from large parameter variations and poor endurance,and these are still obstacles in building circuits for artificial neuron and simulation of synaptic.This thesis investigated the resistance mechanism and regulation of volatile and non-volatile memristors based on the material properties of HfO_x and the effect of embedded nano-islands on their electrical performances,mainly accomplished the following research results:（1）The cross-point structure devices were prepared by the photolithography process,and volatile threshold switching devices of a single layer hafnium oxide film and active electrode Ag were prepared by the plasma-enhanced atomic layer deposition,the threshold switching behaviors of devices could be observed.The forming process of the Au/Ag/HfO₂（4 nm）/Ag NIs/Au device was eliminated by using embedded Ag nano-islands,and the threshold voltage of device was reduced,moreover,the mechanism of volatile threshold switching device based on hafnium oxide was analyzed by combining the electrical properties and material characterization results.The results show the effects of the enhanced electric field induced by the embedded Ag nano-islands,the oxygen vacancy distribution of the hafnium oxide layer was altered,the excessive silver diffusion during forming process was avoided by the elimination of forming process,the endurance was increased to over 5000 pulse cycles.The embedded Ag nano-islands could improve the switching performance of hafnium oxide based volatile threshold switching devices and increases their endurance.（2）In order to limit the amount of silver ions in the dielectric layer to further improve the endurance and other performances of devices,the HfO_x:Ag film was prepared by co-sputtering using the magnetron sputterer with multiple targets,and the HfO_x:Ag film was analyzed by combining X-ray photoelectron spectroscopy,X-ray diffraction,and atomic force microscope.Based on HfO_x:Ag film,the single layer structures of Pt/HfO_x:Ag/Pt and Pt/HfO_x:Ag/Pt NIs/Pt volatile threshold switching devices and the multilayer structures of Pt/HfO₂/HfO_x:Ag/Pt and Pt/HfO₂/HfO_x:Ag/Pt NIs/Pt volatile threshold switching devices were prepared.Comparative analysis of the electrical properties of devices,the results show that the endurances of Pt/HfO_x:Ag/Pt NIs/Pt and Pt/HfO₂/HfO_x:Ag/Pt NIs/Pt devices exceeded 8000 and 104 pulse cycles,respectively,the coefficients of variation of threshold voltage of devices were 8.55% and 9.13%,respectively,so the combination of embedded Pt nano-islands and HfO_x:Ag film could avoid the formation of stable silver conductive filaments in the dielectric layer of devices,and improved the endurance and electrical parameter distribution of HfO_x-based threshold switching devices.（3）The Pt/Ta₂O₅/HfO₂/Pt NIs/TiN and Pt/TaO_x/HfO₂/Pt NIs/TiN devices were prepared by magnetron sputtering and atomic layer deposition,with the help of the X-ray photoelectron spectroscopy results,it was concluded that devices based on magnetron sputtering preparation of TaO_x thin films had high oxygen vacancy concentrations.Combined with the electrical performance measurement results of devices,the results show that the Pt/TaO_x/HfO₂/Pt NIs/TiN non-volatile device prepared by magnetron sputtering of TaO_x thin films had large switching ratios（¹03）and high retention（>105）;the Pt/Ta₂O₅/HfO₂/Pt NIs/TiN non-volatile device prepared by atomic layer deposition of Ta₂O₅ thin films had low SET voltage coefficient of variation（6.46%）,and the stable SET and RESET operations in positive and negative voltage sweeps.