Research On Resisitive Switching And Ferroelectric Properties Of La Doped BiFeO₃ Sputtered Films

With the development of the information age,the demand for information storage of human society is increasing,which greatly promotes the research progress of new storage technologies and new storage materials.Bi Fe O₃(BFO),a lead-free perovskite material,is one of them and has quickly attracted the attention of scholars due to its excellent multiferroic properties at room temperature and the resistive properties discovered in recent years.However,the volatile Bi and the variable valence of Fe restrict its application and development.Fortunately,through continuous research,it has been found that the above problems can be solved to a certain extent by doping.Because of the similar ionic radius of La³⁺and Bi³⁺,La³⁺can effectively replace the doped Bi site,reduce the volatilization of Bi element,improve the film quality and enhance the material performance,which makes BFO has a great application potential in non-volatile memories,such as ferroelectric memories and resistive random access memories.In this dissertation,Pt/La_xB_1-xFe O₃(x=0,6.25at%,12.5at%)/Ti N/Si devices are prepared onto Ti N/Si substrates compatible with CMOS technology by magnetron sputtering technology which is easy for large-scale fabrication.The surface morphology and chemical composition of functional layers of La_xB_1-xFe O₃are characterized by microscopic characterization means and the resistive switching properties of La_xB_1-xFe O₃based devices are tested using semiconductor characteristic analyzer.The results show that La doping effectively improves the resistive switching performance of BFO films,reduces the operating voltage of the devices,obtains more stable cycle tolerance,and better high and low resistance retention ability and pulse fast erasing ability;In the research of resistive switching mechanism,the three different La doped BFO devices conform to the conductive wire model at low resistance state and SCLC model at high resistance state.Moreover,the ferroelectric performance test results show that La doping also increases the remanent polarization,reduces the coercive electric field and the leakage current.Finally,the ferroelectric properties of La-doped BFO films are calculated using the first-principles calculation tool and Berry phase method based on the ferroelectric experiments,and it is found that the spontaneous polarization intensity of BFO increases at first and then decreases as the La dopig content mainly due to the deviation of Bi³⁺and Fe O₆ along the[111]crystal axis caused by the hybridization between La-4f orbit and Bi-6p and O-2p orbits.