Research On Resistive Switching Properties Of BiFeO₃ Thin Films

At present, the Flash memory device is the most popular non-volatile memories(NVM).But now it has to face its bottlenecks, such as low write spead, low density, high write voltages and hard of scaling.Sientists have done a lot of works about the next generation new NVMs to find some divices that have high density, low power waste, high speed and low cost, including magneti random access memory(MRAM), ferroelectric random access memory(FRAM), phase change random access memory(PRAM) and resistance change random access memory(RRAM).Through applied additional voltage on RRAM devices, it is realized that the resistance of RRAM devices will be switched between high resistance state(HRS) and low resistance state(LRS).Comparing with the other three new non-volatile memories, RRAM has simple structure, high speed, low power waste and it can solve the further scaling problem, at the same time the RRAM display high retention characteristics and outstanding data storage capacity. In addition, RRAM technology can fulfill 3-dimensional stack structures.This makes RRAM the most prospecting device in the next generation NVMs. BiFeO3(BFO) is currently the most investigated multiferroic material that shows resistive switchin behavior due to the potential application for NVMs.BiFeO3 thin film based RRAM cells were fabricated by Pulsed Laser Deposition(PLD). The phase composition, micro morphology and electrical properties of BiFeO3 thin film were characterized, respectively. Through a series of experiments, we study the influence of tempreture, oxygen partial pressure and film thickness on the structure and resistive switching properties of the BFO films. By optimizing the preparation process, we got the pure and compact BFO thin films with good resistive switching property at 625 ℃and 1.5 Pa oxygen partial pressure.The results show that BFO thin films have obvious bipolar resistive switching behavior, each of the resistance state can remain 104 seconds at least and can endure times of I-V sweep.There have been many reports on the resistive switching behavior of BFO, however, only a few reports focused on its resistive switching mechanism.This problem influences the application of RRAM in practice seriously. In this paper, we tried to explain the resistive mechanism through the resistive switching behavior of BFO.According to the experiment results, the structure and resistive switching behavior of BFO are influenced by deposition temperature, oxygen partial pressure and film thickness.At wrong temperature, the crystalinity and density of BFO is not well. When the oxygen partial pressure is too low or too high, the oxygen vacancies in BFO films destabilized the resistive properties.With the increase of film thickness, the resistive properties going well.Considering the impact on device density, we need to find a suitable thickness.