| CoFe2O4 is a typical ferrite material with inverse spinel structure and it's unique magnetoelectric properties provide the possibility to realize multi-level storage of memristors.Therefore,it is of far-reaching significance to study the resistive characteristics of CFO films in depth.Hitherto,there has been little research on the resistance characteristics of CFO films,especially CFO films prepared by magnetron sputtering.Compared with other coating methods,magnetron sputtering has the advantages of easy control,dense and uniform film formation,good adhesion,and easy mass produce.Consequently,it is becoming more and more urgent to fabricate CFO film-based resistive switching devices with sputtering technology and improve their resistive performance.In this paper,CFO films of different thicknesses were deposited onto Ti N substrates and Pt/CFO/Ti N resistive switching devices were prepared by lithography subsequently.Furthermore,the morphology,microstructure and component of CFO films were characterized using modern analytical and characterization techniques of AFM,XRD,EDS,XPS and the electrical properties of CFO devices were tested by semiconductor characteristic analyzer.Moreover,the experimental results showed that reducing the film thickness can reduce the set operating voltage and its distribution range,and the low resistance state is relatively more stable.However,the high-resistance state of the low-filmthickness device exhibits a relatively obvious downward trend after multiple pulse cycles,and the fatigue resistance is relatively insufficient.A small pulse of 1.5V amplitude and25 ns pulse width can make the CFO resistive switching device successfully implement the set operation,indicating that the CFO material responds very quickly to the set process.The electrical properties of CFO resistive switching devices with different upper electrode materials(Ti N,Pt,W)were analyzed,showing that set operating voltage of Ti N/CFO/Ti N devices is the smallest and that of W/CFO/Ti N devices is the largest and the on-off ratio of Ti N/CFO/Ti N devices can be maintained above 200.Test result of pulse cycle characteristics and 85? accelerated life retention characteristics showed that Ti N/CFO/Ti N device can be rewritten many times and present good stability of high and low resistance state.The electrothermal coupling simulation model of Ti N/CFO/Ti N devices,based on the oxygen vacancy conductive filament type,were established using the multiphysics finite element analysis software COMSOL and the distribution of oxygen vacancy concentration,potential and temperature during reset and set process were also analyzed in detail.Furthermore,the thickness of CFO film and top electrode material were introduced to the electrothermal coupling model and the simulation results indicate that the simulated I-V curves are consistent with the experimental measurement results,and the CFO devices with upper electrode of low thermal conductivity show low operating voltage and fast resistance change probably due to the rapid migration and reconstruction of oxygen vacancies inside the device driven by the heat accumulation and the temperature rise. |
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