Research On Switching Characteristics And Mechanism Of Y₂O₃ Based Resistive Random Access Memories

Although flash memory have acquired great achievement in nonvolatile storage system,they may not be able to meet future storage requirements for internet of things and artificial intelligence technologies.In special,they demonstrate a pivotal disadvantage due to the unable shrunken storage cell,which limits the sustainable development in the data explosion era.Fortunately,resistive switching(RS)memories,possessing high integration density,high fabrication compatibility,fast switching speed and good retention properties,are regarded as the next generation non-volatile memories.Many thin-film materials,combing with various electrodes,have been utilized to construct the RS memory devices,such as rare-earth metal oxide,two-dimensional thin film material,perovskites,binary transition metal oxides like HfO2,TiO2,TaOx and ZrO2.Among them,yttrium oxide(Y2O3),as a new promising switch material,has attracted much attention in recent years.As known,Y2O3 demonstrates excellent electrical properties,including the wide band gap of 5.6 eV,low leakage current,good thermal stability,and high breakdown voltage.In special,non-crystalline Y2O3 is inherently rich in defects(oxygen vacancies),and hence,it demonstrates great potential for oxygen ions migration-based RS memory applications.In this work,amorphous Y2O3 films are prepared by magnetron sputtering coating method.The properties and mechanism of Y2O3 based resistive memory are studied by focusing on the effects of electrode materials,doping and annealing on resistive memory.The main contents are as follows:1.Amorphous Y2O3 films were prepared by magnetron sputtering method,and RS memory devices with four different electrode structures,Pt/Y2O3/Pt,Al/Y2O3/Pt,Pt/Y2O3/ITO,Al/Y2O3/ITO,were constructed.All devices exhibit bipolar nonvolatile RS behavior,and the switching phenomena are depended on the formation/breaking of oxygen vacancy conducting filaments(CFs)within the film.Among them,Y2O3 based memory with Pt/Y2O3/Pt structure has excellent switching performance,including ultra-low Set/Reset voltage and high hold characteristics.In addition,the effects of different electrodes on the concentration and morphology of oxygen vacancy conducting filaments are discussed in detail.Furthermore,the influence of different electrodes on oxygen vacancies,as well as morphologies of CFs,are discussed in detail.Besides that,physical models are proposed to further clarify carrier transport mechanisms and switching behaviors for memories with different structure.2.Mg-doped Y2O3 films were prepared by magnetron double-target cosputtering method,and the devices of Pt/Y2O3:Mg/Pt structures were constructed.The electrical performance of the doped devices were tested.The results show that the concentration of oxygen vacancy in the oxide film increases after Mg doping in the resistive layer,and the high resistance state of the devices increase significantly.The carrier transport mechanisms of the resistive memory in the high resistance state(HRS)and the low resistance state(LRS)were analyzed.The device belonged to the space charge-limited current mechanism(SCLC)in the HRS and the ohm conduction mechanism in the LRS.3.Pt/Y2O3:Pt/Pt devices were prepared by using Y2O3 ceramic target as sputtering source and Pt doped by double target co-sputtering.Y2O3 devices prepared by ceramic target sputtering show large and dispersed threshold voltage,which leads to high power consumption and high probability of misreading.However,when Pt enters Y2O3 films as dopant,the forming process of the device disappears,and the threshold voltage is significantly reduced and the distribution is more concentrated,showing good RS performance.4.The Y2O3 films were annealed in nitrogen filled environment and then prepared into devices with Al/Y2O3/ITO structure.During the Reset process,the resistance value changes from abrupt change to gradual change,and the device has high electrical stability.The conduction mechanism of the device HRS and LRS belongs to trap-controlled SCLC mechanism and ohm conduction mechanism respectively.This method provides a new way for the transition from mutant memory to gradual artificial synaptic simulation and lays a foundation for future research.