Investigation Of Properties And Working Mechanism Of Traps Of Perovskite Thin Films For Resistive Random Access Memory

As a new type of non-volatile memory,resistance random access memory(RRAM)is one of the frontiers and advantages of international storage technology because of its outstanding properties,including high on/off ratio,high speed,low power consumption,and etc.A commonly used material for resistive memory is a perovskite thin film.BFO and BWO films have attracted much attention in resistance and ferroelectric memory because of its ferroelectricity and high on/off ratio.Currently,the development of RRAM has been restricted due to unclear resistive(RS)effect and failure mechanism.The conductive mechanism of RRAM can be divided into conductive filament mechanism and interface barrier mechanism.Either mechanism is related to the traps and defects of the resistive thin film.The number and location of traps and defects inside the resistive film will change in the process of using.And it will affect the RS effect and lifetime of the RRAM.Researchers have done a lot of research on the resistive and trap mechanism of perovskite resistive thin film to promote the commercial application of RRAM.In this thesis,we study the mechanism of resistiance and trapping of perovskite thin film RRAM.The mechanism of resistiance and conduction of BFO and BWO thin films are studied to explain the trap mechanism.The research study the trap characteristics of BFO thin film.And revealing the change of traps in the fatigue process.The feasibility of BWO thin films in RRAM and perovskite solar cells was studied through fatigue and aging experiments.The main works are as follows:(1)The BFO thin films is Au/Bi Fe O₃/Sr Ru O₃ sandwich structure as basic memory cell of the variable memory.The conductive mechanism is space charge limited conduction.The RS effect is related to the trapping/detrapping behavior of trap center.We measured a new trap time constant?₂ and trap level E?2=0.29±0.02e V by transient current method in the low temperature environment(253K).The mechanism of trap behavior is revealed and expand the application range of transient current method.(2)Study the trap level mechanism of BFO thin film by transient current method in low temperature fatigue process.At the beginning of fatigue,the locked polarization domains of the ferroelectric thin films are set free by the wake-up effect.Due to the release of ferroelectric domains,the upward polarization ordering increases,and the time constant and the number of trap levels increase.The trap density increases after polarization wake-up,the traps become less and less full,the structure around the traps becomes less ordered,and the time constant decrease.As the number of switching cycles further increases,more and more traps are generated and are randomly distributed throughout the film.This leads the trap levels to merge and part of the time constant disappears.Finally,the leakage current of BFO thin film increases rapidly,the RS effect disappears and the film is deviced.(3)The sandwich structure of Pt/Bi₂WO₆/Sr Ru O₃ thin film has RS effect with high on/off ratio(10²).BWO film can be used as a RRAM due to its excellent data retention and fatigue characteristics.The planar structure of Pt/Bi₂WO₆/Sr Ti O₃ film has photoelectric effect.The BWO perovskite solar cells exhibit excellent high temperature stability in the 400-hour high-temperature aging test.