Investigation Of The Characterization And Working Mechanism Of Traps In Ferroelectric Thin Film Devices

Resistive random access memory?RRAM?has become one of the most promising next generation non-volatile memories because of its low power consumption,high density,simple structure and easy compatibility with CMOS technology.The resistive switching?RS?mechanism of RRAM can be divided into two types.The first type is the conductive filament model,in which resistive switching results from the formation and rupture of a conductive path.The second type is the interface barrier model,in which the Schottky barrier formed between the ferroelectric film and the metal electrode can be modified to produce the RS effect.Defects always play an important role in both of the RS mechanism.The generation and movement of defects always affect the reliability and shorten the service life of devices.In order to realize the industrialized production of RRAM,researchers have carried out extensive research on the mechanism of the traps in RRAM,and made a deep exploration on the characterization and analysis of the traps in devices.In this paper,we mainly investigated the traps in RRAM,characterized the traps of the device in situ,understood the mechanism of the traps in the RS process,studied the effect of the traps on the device reliability and deep understood the RS mechanism of the device,which lay a foundation for the commercial production of RRAM.The specific research contents are as follows:?1?The experimental sample is the basic resistive storage unit of Au/BiFeO₃/SrRuO₃ sandwich structure.The RS effect is mainly controlled by the trapping/detrapping of charge carriers.By analyzing the transient current of the device and extracting the trap time constant,we measured the trap energy level of oxygen vacancy Ea=0.71±0.06 eV.At the same time,the relationship between trap filling state or polarization state and trap time constant is analyzed,and the mechanism of trapping/detrapping of charge carriers is revealed.?2?The RS mechanism can be controlled by the movement of oxygen vacancies and trapping/detrapping of charge carriers.When we continuously applying a-15 V voltage to the sample,the oxygen vacancy in the film moved towards the Au/BiFeO₃interface,and a RS-reversal effect occurred.The retention behavior of the stressing sample can be increased about 30%compared with the virgin sample.The change of oxygen vacancy concentration at the barrier boundary can also affects the trap density,trap level and trapping ability of the device.By analyzing the capacitance-voltage?C-V?curve of the device,the relationship between the trap density and the free carrier concentration can be obtained.?3?The fatigue process of the RRAM can be divided into two stage:wake up stage and fatigue stage.In the wake-up stage,the released polarization can make the trap density increase,the characteristic parameter of the device was enhanced at the same time.In the fatigue stage,the RS effect and the ferroelectric properties was reduced.The oxygen vacancy and free carrier concentration increased with the decreasing performance of the device.