Preparation And Properties Of Resistive Switching Devices Based On BFO Thin Film

With the rapid development of big data and artificial intelligence in recent years,the performance of storage technology is increasingly demanded.The resistive memory is not only simple in structure,but also has the advantages of low power consumption,high storage density,small size and easy large-scale integration.Wherein,Write-once-read-many-time memory（WORM）,with the characteristic that the data cannot be changed or deleted once written,is suitable for applications that need stable and long-term archiving of information,images and videos,and has broad development potential in next generation of new non-volatile memory.BiFeO₃（BFO）,one of the few single-phase multiferroic materials with both ferroelectricity（FE）and antiferromagnetism（AF）at room temperature,has attracted the interest of many researchers.Recently,the resistive switching characteristics of BFO have attracted people’s interest.However,most research works focused on the bipolar resistance switch of BFO thin films,while rarely reported on the WORM resistive switching characteristics.In this thesis,we focused on the preparation of BFO thin films and the design of devices,and studied its potential application in WORM.The main research works are as follows:（1）Preparation of high crystalline quality BFO thin films on the surface of La Ni O₃（LNO）thin films.The technological parameters of preparing LNO thin films with smooth surface and good conductivity were studied by using magnetron sputtering combined with O₂annealing in tube furnace.The effects of different annealing conditions on the crystallinity and surface morphology of BFO films were studied.It was found that the films annealed with O₂showed a preferred orientation of（100）.Among them,BFO films deposited at400℃and annealed at 650℃show good crystallinity,smooth surface,and almost no pinhole.（2）Designing and fabricating resistive switching devices with metal electrode/BFO/LNO sandwich structure.The BFO thin film with a thickness of 150 nm was prepared and the Pt electrode with a diameter of 200μm was prepared by electron beam deposition.The structure and resistance switching characteristics of BFO films with different O₂annealing temperatures（500℃,550℃,600℃,650℃and 700℃）were analyzed.The results indicate that all the crystalline BFO films at the annealing temperature above 600℃show stable WORM resistive switching characteristics with the stability exceeding 3600 s and the durability reaching 1000 cycles.Among which the samples annealed at 650℃showed extremely high ON/OFF ratio（>3×10⁴）.The conduction mechanism of the device before and after resistive switching is controlled by SCLC and ohmic conduction mechanism respectively,and the WORM characteristic is attributed to the permanent formation of conductive filaments.（3）The effects of different BFO thickness and electrodes on the device performance.The devices with different BFO thin film thicknesses showed stable WORM characteristics,but the ON/OFF ratio of the device decreased obviously with the decrease of thickness.Different top electrodes were prepared on the surface of BFO thin film to explore the influence of different electrodes on the resistive switching characteristics.The devices using Ag and Cu as top electrodes still showed WORM resistive switching characteristics,while the conduction mechanism was dominated by Schottky emission.Nevertheless,the devices using Al as top electrodes did not demonstrate resistive switching characteristics,but showed the phenomenon of current hysteresis.