The Nonvolatile Bipolar Resistive Switching Characteristics Of Hydrothermal Epitaxial Perovskite Films

Resistance random access memory?RRAM?can achieve data storage by switching between high and low resistance states.It is regarded as the next generation non-volatile memory due to its characteristics of simple structure?metalsemiconductor/insulator-metal?,non-destructive way of data storage,non-volatile characteristics,low energy consume,high density and operation speed.The non-volatile resistive switching behavior is closely related to medium layers in RRAM devices.Recently,the excellent resistive switching behavior has been observed in various materials.Therein,perovskite structure materials,as a kind of function materials with unique physical and chemical properties,have attracted great interest in RRAM.They are contributed to the pluralism and integration of RRAM devices.Although so many conductive mechanisms of perovskite materials have been proposed,the debates of mechanisms have been inconclusive.The design,control and application of perovskite oxide materials can not be perfectly realized due to the lack of a universal physical mechanism in the RRAM field.In this thesis,we focus on the perovskite or perovskite-like materials,CaTiO₃,Bi Fe O₃ thin films and?CH₃NH₃?₂Fe Cl₄?MAFC?crystals,to systematically research the conductive-state switching mechanism.In our works,hydrothermal epitaxy is firstly adopted to fabricate these perovskite medium layers?CaTiO₃,Bi Fe O₃ thin films?due to the advantages of lower temperature and higher pressure.The main research results are summarized as follows:1.Based on the high quality of CaTiO₃ hydrothermal films,the excellent bipolar resistive switching behavior is observed in Pt/CaTiO₃/Nb:Sr Ti O₃ cells.This conductive-state switching characteristics can be explained by the trap-controlled space charge limited current?SCLC?conduction mechanism.And the abundant oxygen vacancies,which exist in hydrothermal epitaxial CaTiO₃ thin films,play a “trap centers” role in the whole process.According to trapping or releasing the injected electrons by oxygen vacancies,the trapping or detrapping process can be completed and the resistive switching characteristics of Pt/CaTiO₃/Nb:Sr Ti O₃ cells are achieved under the sweeping voltage.2.In order to verify the universality of SCLC mechanism in other perovskite oxide hydrothermal epitaxial films,we fabricate the good quality of Bi Fe O₃ thin films.The tri-state bipolar resistive switching behavior is firstly observed in Pt/Bi Fe O₃/Nb:Sr Ti O₃ devices.And the conductive mechanism can also be explained by SCLC mechanism.Meanwhile,the modulation of the Pt/Bi Fe O₃ Schottky-like barrier under an applied electric field is also responsible for the switching behavior in the carrier injection-trapped/detrapped process.This work sets up the experimental foundation for multilevel storage.3.Based on the above two works,we prepare the high crystalline perovskite-like material of MAFC.The stable non-volatile bipolar resistive switching characteristics are firstly observed in Ag/MAFC/Cu cells.The conductivity-state switching behavior is derived from the competition between the ionic current within the MAFC and Faradaic current that is originated from redox processes at the Ag/MAFC/Cu interfaces.4.In the above work,we notice considerable field dependence of the magnetization in the MAFC crystals.And the weak ferromagnetic and antiferromagnetic orders are coexisted in the MAFC.These results are related to the spin canted antiferromagnetic transition due to the long-distance super exchange of MAFC under the applied magnetic field.Meanwhile,the ferroelectric polarization can be achieved under the applied electric field.The coexistence of the magnetic and electric orders provides a new path to study single phase multiferroic materials.