The Study On Resistive Switching Characteristics For LiFePO₄ Memory Devices

As a promising candidate for next-generation nonvolatile storage technology, resistive random access memory(RRAM) is attracting great attention due to superior performance characteristics, such as simple structure, high density, fast programming speed, low power consumption, good retention. Recently, some lithium ion battery cathode material has been used as the switching layer to realize the resistive-switching(RS) behavior, based the migration of Li ion resulting the redox process. In this paper, we chose Li Fe PO4 as switching layer due to its lower conductivity and good stability. Meanwhile, we also studied the RS performance and mechanism for the Li Fe PO4 RRAM device.Herein, the Li Fe PO4 RRAM devices were fabricated by magnetron sputtering and evaporation methods, meanwhile, the effects of different annealing temperature and bottom electrodes have been further studied for the RS phenomenon. According to the optimizing, we chose the Au/Li Fe PO4/C(graphite sheet) device with 600°C annealing temperature, and further studied its RS characteristics. Typical bipolar RS with good performance is demonstrated in the Au/Li Fe PO4/C memory device. It has the fast programming speed, small switching voltage, good endurance, the long time retention characteristic, high uniformity and controllability, which are very important for practical application of RRAM. Meanwhile, some reversible and steady resistance states are observed by changing compliance current or resetting voltage. These phenomena indicate that the device can be used to realize multilevel memory. All the resistance states exhibit similar semiconductor temperature dependence characteristics as the initial state film. Further, by comparing their activation energy,we found that the activation energy of electrons decreases gradually as the resistance decreases. we speculate that Li+ can transfer under the electric field,with the decrease of resistance may reduce the concentration of Li in conductive channel,resulting in the increase of related defects,which reduces the activation energy of the electronic. Finally, by adopting secondary ion mass spectroscopy we probe the content of Li on devices of depth profile,we found that the content of Li is distinct in graphite sheets in HRS and LRS,certified Li migration model. Therefore, The Li migration model can to explain the RS behaviors of Au/Li Fe PO4/C memory device.Between the Li Fe PO4 and the graphite sheet Li+ can transfer reversible under the field, to realize the gradually change of Li concentration in the conductive channel,to achieve multi-level resistance state storage.